Biochemistry of Integumen

Biochemistry of IntegumenMed Biochemistry DepartementExtracellular MatrixThe space between the cells (the interstitium) is occupied by a substance with a complex composition known as the extracellular matrix (ECM) and has a very wide variety of functions: establishes mechanical connections between cells; creates structures with special mechanical properties (as in bone, cartilage, tendons, and joints); creates filters (e. g., in the basal membrane in the renal corpuscles; separates cells and tissues from each other (e. g., to allow the joints to move freely); provides pathways to guide migratory cells (important for embryonic development). The chemical composition of the ECM is just as diverse as its functionsextracellular matrixMost mammalian cells are located in tissues where they are surrounded by a complex extracellular matrix (ECM) often referred to as connective tissuethree major classes of biomolecules: the structural proteins, collagen, elastin, and fibrillin; specialized proteins such as fibrillin, fibronectin, and laminin;proteoglycans,Organisasi ECM

Best-defined ECMBasement membrane (lamina basalis): lembaran setebal 50-200 nm: (1) mengelilingi otot dan sel2 lemak (2) mendasari jaringan epithel di sepanjang saluran pencernaan dan pernafasan (3) terdapat pada bagian endotel dalam pembuluh darah CollagenTheir characteristic properties are tensile strength and flexibilitySebuah serat kolagen dengan diameter 1 mm menahan beban seberat 10 kg (tidak putus).Merupakan protein terbanyak dalam tubuh manusia (25%)Terdapat lebih dari 27 jenis kolagen dalam tubuh manusia.

Collagen..The triplet Gly-X-Y is constantly repeated inthe sequence of the triple-helical regions, every third amino acid is a glycine. Proline (Pro) is frequently found in positions X or Y.Y position is often occupied by 4-hydroxyproline (4Hyp), although 3-hydroxyproline (3Hyp) and 5-hydroxylysine (5Hyl) also occur. The various types of collagen consist ofdifferent combinations of -chains (1 to 3and other subtypes)

Collagen (Cont.)Dua karakteristik utama, yaitu: (1) merupakan trimer yang terdiri atas 3 rantai polipeptida ( chain) (2) Ketiga rantai polipeptida saling melilit membentuk triple helix yang unik

Figure 7.6 Struktur Kolagen. (a) Monomer kolagen merupakan triple helix, homotrimers, maupun heterotrimers (b) Molekul2 kolagen berjajar membentuk serat kolagen (collagen bril.) (c) serat kolagen manusia (d) permukaan serat kolagen. Komponen penyusun kolagen saling melilit membentuk struktur seperti tali

Collagen (Cont.)Tendon : menghubungkan otot dan tulangStroma kornea: mengandung serat kolagen Mutasi pada gen kolagen tipe 1 menyebabkan tulang rapuh, kulit tipis, tendon lemah, dapat menyebabkan kematianMutasi pada gen kolagen type 2 (jaringan kartilago) menyebabkan deformitas skeletal, kekerdilanMutasi lainnya: hyperfleksibilitas sendi, highly extensible skin (EhlerDanlos syndromes). CollagenAbout 30 genes encode collagen a number of diseases are due to mutations in collagen genes or in genes encoding some of the enzymes involved in these posttranslational modifications. The diseases affecting bone (eg, osteogenesis imperfecta) and cartilage (eg, chondrodysplasia)

Ehlers-Danlos syndromeEhlers-Danlos syndrome comprises a group of inherited disorders whose principal clinical features are hyperextensibility of the skin, abnormal tissue fragility, and increased joint mobility. 10 types have been recognized, Type IV is the most serious because of its tendency for spontaneous rupture of arteries or the bowelPatients with type VI, due to a deficiency of lysyl hydroxylase, exhibit marked joint hypermobility and a tendency to ocular rupture. A deficiency of procollagen N-proteinase, causing formation of abnormal thin, irregular collagen fibrils, results in type VIIC, manifested by marked joint hypermobility and soft skin.Alport syndromeAlport syndrome is the designation applied to anumber of genetic disorders (both X-linked and autosomal) affecting the structure of type IV collagen fibersThe Major collagen found in the basement membranes of the renal glomeruli The presenting sign is hematuria, and patients may eventually develop end-stage renal disease. Electron microscopy reveals characteristic abnormalities of the structure of the basement membrane and lamina densa

Alport syndromethe skin breaks and blisters as a result of minor trauma.The dystrophic form is due to mutations in COL7A1, affecting the structure of type VII collagen. This collagen forms delicate fibrils that anchor the basal lamina to collagen fibrils in the dermis. These anchoring fibrils have been shown to be markedly reduced in this form of the disease, probably resulting in the blistering.Epidermolysis bullosa simplex, another variant, is due to mutations in keratin 5ElastinElastin is a connective tissue protein that is responsible for properties of extensibility and elastic recoil in tissues. Although not as widespread as collagen, elastin is present in large amounts, particularly in tissues that require these physical properties, eg, lung, large arterial blood vessels, and some elastic ligaments. Smaller quantities of elastin are also found in skin, ear cartilage, and several other tissues. In contrast to collagen, there appears to be only one genetic type of elastinElastin is synthesized as a soluble monomer of 70 kDa called tropoelastin.

ElastinAfter secretion from the cell, certain lysyl residues of tropoelastin are oxidatively deaminated to aldehydes by lysyl oxidase, the same enzyme involved in this process in collagen. However, the major cross-links formed in elastin are the desmosines, Once cross-linked in its mature, extracellular form, elastin is highly insoluble and extremely stable and has a very low turnover rate. Elastin exhibits a variety of random coil conformations that permit the protein to stretch and subsequently recoil during the performance of its physiologic functions.

ElastinDeletions in the elastin gene (located at 7q11.23) have been found in approximately 90% of subjects with Williams syndrome, a developmental disorder affecting connective tissue and the central nervous system.The mutations, by affecting synthesis of elastin, probably play a causative role in the supravalvular aortic stenosis often found in this condition.skin diseases (eg, scleroderma) are associated with accumulation of elastin.Fragmentation or, alternatively, a decrease of elastin is found in conditions such as pulmonary emphysema, cutis laxa, and aging of the skin.FibrilinFibrillin is a large glycoprotein (about 350 kDa)structural component of microfibrils, 10-12 nm fibers Fibrillin is secreted into the extracellular matrix by fibroblasts Marfan syndrome: fibrillin is found in the zonular fibers of the lens, in the periosteum, and associated with elastin fibers in the aorta (and elsewhere); these locations respectively explain the ectopia lentis, arachnodactyly, and cardiovascular problems found in the syndrome. FibronectinFibronectin is a major glycoprotein of the extracellular matrix,It consists of two identical subunits, each of about 230 kDa, joined by two disulfide bridges near their carboxyl terminals. The gene encoding fibronectin is very large, containing some 50 exonsFibronectin contains three types of repeating motifs (I, II, and III), which are organized into functional domains, functions of these domains include binding heparin and fibrin, collagen, DNA, and cell surfaces. FibronectinFibronectin contains an L-arginine, glycine, and L-asparticArg-Gly-Asp (RGD) sequence that binds to the receptor. The RGD sequence is shared by a number of other proteins present in the ECM that bind to integrins present in cell surfaces. Synthetic peptides containing the RGD sequence inhibit the binding of fibronectin to cell surfaces.

FibronectinFibronectin, terdiri atas serangkaian modul.Setiap polipeptida bronectin dibangun dari ~ 30 modul Fn.Fn-type modules pada bronectin merupakan bagian dari berbagai protein, mulai dari faktor pembekuan darah hingga reseptor membran

Figure 7.10 Struktur bronectin. (a) Molekul bronectin manusia terdiri atas 2 polipeptid non identik yang disatukan oleh sepasang ikatan disulde dekat carboxyl terminal. Setiap polypeptide tersusun atas Serangkaian modul berbeda yang terorganisir menjadi unit2 domain fungsional (silinder berwarna). Setiap unit fungsional terdiri atas 1 atau lebih tempat pengikatan bagi komponen spesifik ECM atau bagi permukaan sel.

The interaction of fibronectin with its receptor provides one route whereby the exterior of the cell can communicate with the interior and thus affect cell behavior. Via the interaction with its cell receptor, fibronectin plays an important role in the adhesion of cells to the ECM. It is also involved in cell migration by providing a binding site for cells and thus helping them to steer their way through the ECM.

Lamininlaminin is a major protein component of renal glomerular & other basal laminas (eg, muscle cells).Basal laminas are specialized areas of the ECM that surround epithelial and some other cells.The primary components of the basal lamina are three proteinslaminin, entactin, and type IV collagenand the GAG heparin or heparan sulfate.LamininLaminin (about 850 kDa, 70 nm long) consists ofthree distinct elongated polypeptide chains (A, B1, and B2) linked together to form an elongated cruciform shape. It has binding sites for type IV collagen, heparin, and integrins on cell surfaces. The collagen interacts with laminin (rather than directly with the cell surface), which in turn interacts with integrins or other lamininreceptor proteins, thus anchoring the lamina to thecells. Entactin, also known as nidogen, is a glycoprotein containing an RGD sequence; it binds to laminin and is a major cell attachment factor.LamininBerperan dalam migrasi, pertumbuhan dan diferensiasi sel.Menuntun ujung axis embrio, berperan dalam migrasi bakal sel germinal yang berasal dari yolk sac, di luar embrio. Sel ini kemudian bermigrasi melalui aliran darah dan jaringan embrio menuju gonad yang sedag berkembang. Di sini sel berkembang menjadi sel sperma atau sel telur.

(a) Figure 7.11 The role of cell migration during embryonic development.ProteoglycansProteoglycan terdiri atas molekul protein inti yang terikat pada rantai glycosaminoglycans (GAGs).Setiap glycosaminoglycan tersusun atas unit berulang disaccharide; dengan struktur -A-B-A-B-A-, (A dan B merupakan 2 gula yang berbeda)Proteoglycans pada ECM terorganisir menjadi gigantic complexes melalui linkage antara protein core terhadap molekul hyaluronic acid, a nonsulfated GAG.Kolagen dan proteoglikan menyebabkan kartilago dan komponen ECM lainnya menjadi kuat dan resisten terhadap deformasi. ECM tulang tersusun atas kolagen dan proteoglikan, namun mengeras dengan adanya garam fosfat kalsium (calcium phosphate salts). Baik GAG bersulfat maupun nonsulfated digunakan sebagai supplement perbaikan kondisi kulit dan persendian.Struktur proteoglikan

GAG - H3O +Hydrated gel with pores resists crushing forcesCollagens and GAGs give cartilage and other ECM strength and resistance to deformation.The GAG chains also act as binding sites for many growth factors, affecting their interaction with cell-surface receptorsGambar 7.9. Kompleks proteoglikanMatrix metalloproteinases (MMPs) ECM bersifat dinamis, komponen penyusun ECM mengalami degradasi dan rekonstruksi.Degradasi ECM dikatalisis oleh enzym dari kelompok MMPsProtein yang mengandung Zinc, disekresi ke dalam ruang ekstracellular atau terikat ke membran plasma.MMP berperan dalam remodelling jaringan, migrasi sel embrionik, penyembuhan luka dan pembentukan pembuluh darah.MMP dilaporkan terkait dengan athritis, atherosclerosis, hepatitis, penyakit gusi dan mulut, tumor.Mutasi pada gen penyandi MMP menyebabkan kelainan skeletal

Interaksi Sel dengan ECMECM (bronectin, laminin, proteoglycans, dan collagen) dpt terikat pada reseptor di permukaan selReseptor membran terpenting dalam hal ini adalah integrin.Integrin terdiri atas 2 rantai polipeptida & , terikat secara non kovalen.Integrin memiliki situs pengikatan Ca2+ pd rantai Rantai dapat mengenali sekuen (tripeptide Arg-Gly-Asp) RGD pada fibronectin

Adhesi pada sel epithelAda 2 macam protein adhesi transmembran, yaitu cadherin, berfungsi sebagai perantara perlekatan antar sel dg sel. Integrin, sebagai perantara perlekatan antar sel dengan matriks.

HemidesmosomePerekatan sel epitel dengan membran basal (membrane basement) *In vivoTipe adesi hemidesmosome merupakan ikatan terkuat antara sel dan ECM dimana sel2 terikat struktur di bawah membran basal.Hemidesmosome mengandung banyak plaque dengan filamen yang terdiri atas keratin (golongan lament intermediat). Keratin terhubung dgn ECM melalui integrin.Integrin berfungsi mentransmisi signal dari ECM sehingga mempengaruhi aktivitas sel epitel.Pentingnya HemidesmosomePemfigus Bulosa: auto antibodi/auto immune antibodi menyerang protein (antigen bullous pemphigoid) pada hemidesmosome. Lapisan bawah epidermis kehilangan pengikatan dengan bagian utama membrana basalis.Kebocoran larutan ke ruang bagian bawah epidermis menyebabkan blistering.Fenotip epidermolysis bullosa disebabkan oleh perubahan pada sejumlah protein hemidesmosome.Hemidesmosomes

Empat family protein integral berperan dalam adesi antara sel dengan sel1. Selectin2. Beberapa anggota IgSF dan integrin3. Cadherin4. Adherene junction dan desmosome: anchoring sel ke sel lainnya1. SelectinSelectins Memiliki domain sitoplasmik kecil dan domain extraseluler besarTiga jenis selektin:E-selectin pada sel-sel endothelial.P-selectin pada platelet dan sel-sel endotelial.L-selectin pada sel-sel darah.

Selectin famili integral membran glycoprotein yang terikat pada gula di permukaan sel.

2. Immunoglobulin dan integrinIg domain: 70-100 asam aminoKebanyakan IgSF memediasi limposit dan makropfage dan mentarget sel untuk respon immune Beberapa IgSF antara lainVCAM, NCAM dan L1 memediasi interaksi antara sel non immune i.e. pembentukan synapse, perkembangan sarafImmunoglobulin superfamily (IgSF)Kebanyakan protein2 dari family ini terlibat dalam fungsi imune.molekul IgSF membantu interaksi lymphocytes dengan sel2 untuk respon immune.

3. Chaderinmerupakan glycoprotein yang memediasi adesi sel dengan sel, (membutuhkan Ca). Juga membantu transmisi signal dari ECM ke cytoplasm. Membantu perubahan adesi selama perkembangan embrio melalui pembentukan epithelial-mesenchymal transition (EMT).

Eg. E-cadherin, N-cadherin, P-cadherinCadherins and the EMT

Eg. E-cadherin, N-cadherin, P-cadherin4. Adheren junction dan desmosome: anchoring sel ke sel lainnyaAdhesive junctions (ca2+dependent): 1.adherens junction 2.desmosomes 3.junctional complexes (tight junction and gap junction)Kompleks junction intraseluler

Intercellular junction complex

Molecular architecture of adherens junction

Desmosome adhesive junction antar sel.Terdapat dalam berbagai jaringan.Mengandung cadherin yang menghubungkan dua sel diantara celah yang sempit.Cadherin desmososme memiliki struktur domain : desmogelins dan desmocollins.DESMOSOMEStruktur desmosome

transfer informasi menyeberangi memban plasma disebut transmembrane signaling.Integrin dan cadherin dapat mentransmit signal dari lingkungan extracellular ke cytoplasm.Peranan Reseptor Adesi sel dalam signaling

Interactions involving the cell surface

Tight Junction: Menutup ruang ExtracellularTerdapat pada bagian paling ujung kompleks junction antar sel.Berperan sebagai barier bagi air dan larutan dari bagian extracellular.Sebagian tight junction bersifat permiabel bagi ion atau larutan tertentu.

Tight junctions

Tight junctions

Gap Junction : berperan dalam Komunikasi InterselulerGap junctions situs pada sel hewan yang untuk komunikasi interseluler.Terbentuk seluruhnya deari protein membran conexin.Conexins terorganisasi menjadi kompleks connexon.

Gap junction

Gap-junction intercellular communication (GJIC) memungkinkan lewatnya molekul dengan berat molekul kecil.Gap junction memungkinkan activitas unit unit sel berintegrasi ke dalam satu unit fungsional.Perbedaan kompatibilitas antara koneksin dapat mendorong atau menghambat komunikasi antara sel2 yang berbeda.Harper's Illustrated BiochemistryColor Atlas of Biochemistry (J. Koolman, K.-H. Roehm)Cell and Molecular Biology: Concepts and Experiments (Wiley)