Cu trc khng gian ca protein[sa|sa m ngun]Protein c 4 bc cu trc c bn:Cu trc bc mt[sa|sa m ngun]Cc axit amin ni vi nhau bi lin kt peptit hnh thnh nn chui polypepetide. u mch polypeptide l nhm amin ca axit amin th nht v cui mch l nhm cacboxyl ca axit amin cui cng. Cu trc bc mt ca protein thc cht l trnh t sp xp ca cc axit amin trn chui polypeptide. Cu trc bc mt ca protein c vai tr ti quan trng v trnh t cc axit amin trn chui polypeptide s th hin tng tc gia cc phn trong chui polypeptide, t to nn hnh dng lp th ca protein v do quyt nh tnh cht cng nh vai tr ca protein. S sai lch trong trnh t sp xp ca cc axit amin c th dn n s bin i cu trc v tnh cht ca protein.Cu trc bc hai[sa|sa m ngun]l s sp xp u n cc chui polypeptide trong khng gian. Chui polypeptide thng khng dng thng m xon li to nn cu trc xon v cu trc np gp , c c nh bi cc lin kt hyro gia nhng axit amin gn nhau. Cc protein si nh keratin, Collagen... (c trong lng, tc, mng, sng)gm nhiu xon , trong khi cc protein cu c nhiu np gp hn.Cu trc bc ba[sa|sa m ngun]Cc xon v phin gp np c th cun li vi nhau thnh tng bi c hnh dng lp th c trng cho tng loi protein. Cu trc khng gian ny c vai tr quyt nh i vi hot tnh v chc nng ca protein. Cu trc ny li c bit ph thuc vo tnh cht ca nhm -R trong cc mch polypeptide. Chng hn nhm -R ca cystein c kh nng to cu isulfur (-S-S-), nhm -R ca prolin cn tr vic hnh thnh xon, t v tr ca chng s xc nh im gp, hay nhng nhm -R a nc th nm pha ngoi phn t, cn cc nhm k nc th chui vo bn trong phn t... Cc lin kt yu hn nh lin kt hyro hay in ha tr c gia cc nhm -R c in tch tri du.Cu trc bc bn[sa|sa m ngun]Khi protein c nhiu chui polypeptide phi hp vi nhau th to nn cu trc bc bn ca protein. Cc chui polypeptide lin kt vi nhau nh cc lin kt yu nh lin kt hyro.Lin kt peptide[sa|sa m ngun]Lin kt peptide (-CO-NH-) c to thnh do phn ng kt hp gia nhm carboxyl ca mt acid amine ny vi nhm - amin ca mt acid amine khc, loi i 1 phn t nc. S phn ng nh sau:Sn phm ca phn ng ny l mt dipeptide. Nu 3, 4, 5 v.v. hoc nhiu acid amine kt hp vi nhau, to thnh cc peptide c cc tn tng ng l tripeptide, tetrapeptide, pentapeptide v.v. v polipeptide.Phn t protein c cu to t 20 L--acid amine cc amid tng ng.Mt s peptide t nhin quan trng:-Glutathione (tripeptide): - glutamyl xistiein glyxinLin kt peptideGlutathione c trong tt c cc c th sng, tham gia cc phn ng oxi ha kh.-Cacnoxin (dipeptide): - alanine histidineCacnozin c nhiu trong c ca ng vt c xng sng (tr mt s loi c), vai tr sinh hc cha c xc nh r nhng c th tham gia cc qu trnh sinh ha khi c hot ng.-Oxytocin v Vasopressin: l cc notropeptide c cu trc c cu trc ha hc c bit sm nht v cng c tng hp ha hc. oxytocin v vasopressin gm 9 acid amine, trong phn t c mt cu disulfua. ngha cu trc bc 1 protein[sa|sa m ngun] L bc u tin quan trng xc nh c s phn t hot tnh sinh hc v tnh cht ha l ca protein. L du hiu r nht v s sai khc gia protein ny vi protein khc. L c s xc nh cu trc khng gian ca phn t protein. T nhng dn liu v cu trc bc I, trn c s nhng quy lut hnh thnh cu trc khng gian protein, da vo cu trc khng gian ca cc protein tng ng, c th d on s nh v cu disulfua, cu trc khng gian ca protein nghin cu. L yu t gp phn quan trng trong nghin cu bnh l phn t. Nhiu kt qu nghin cu cho thy khi thay i th t acid amine, thm ch thay i ch 1 gc acid amine trong phn t protein c th lm thay i hot tnh sinh hc, chc nng ca mt c quan. Cu trc bc I l bn phin dch m di truyn. V vy, cu trc ny ni ln quan h h hng v lch s tin ha ca th gii sng. Vic xc nh c cu trc bc I l c s tng hp nhn to protein bng phng php ha hc hoc cc bin php cng ngh sinh hc.S hnh thnh bn bc cu trc protein[sa|sa m ngun]Do cch lin kt gia cc acid amine to thnh chui polipeptide, trong mch di polipeptide lun lp li cc on CO-NH-CH-Mch bn ca cc acid amine khng tham gia to thnh b khung ca mch, m bn ngoi mch polipeptide.Kt qu nghin cu ca Paulin v Cori (Linus Pauling, Robert Corey 1930) v nhng ngi khc cho thy nhm peptide (CO-NH-CH-) l phng v cng.H ca nhm NH- lun v tr trans so vi O ca nhm carboxyl. Nhng nhm peptide c cu trc hnh phng, ngha l tt c cc nguyn t tham gia trong lin kt peptide nm trn cng mt mt phng. Paulin v Cori xc nh c khong cch gia N v C ca lin kt n (1,46 AO) v khong cch gia C v N trong khng gian. Trong lin kt i C=N-, khong cch ny l 1,27 AO. Nh vy, lin kt peptide c mt phn ca lin kt i, c th hnh thnh dnh enol nh sau:Do lin kt peptide cng, khng c s t do quay xung quanh lin kt ny. Ngc li, kh nng quay t do xung quanh cc lin kt ni nhm peptide vi cc carbon xung quanh (gia C v C, gia N v C) l rt ln, mch peptide c khuynh hng hnh thnh cu trc xon.Cu trc bc mt: Chui acid amine c bn[sa|sa m ngun]T cc acid amin, nh lin kt peptid ni chng li vi nhau to nn chui polypeptid:Chui polypeptid l c s cu trc bc I ca protein. Tuy nhin, khng phi mi chui polypeptid u l protein bc I. Nhiu chui polypeptid ch tn ti dng t do trong t bo m khng to nn phn t protein. Nhng chui polypeptid c trt t acid amin xc nh th mi hnh thnh phn t protein. Ngi ta xem cu to bc I ca protein l trt t cc acid amin c trong chui polypeptid. Th t cc acid amin trong chui c vai tr quan trng v l c s cho vic hnh thnh cu trc khng gian ca protein v t qui nh c tnh ca protein. Phn t protein bc I cha c hot tnh sinh hc v cha hnh thnh nn cc trung tm hot ng. Phn t protein cu trc bc I ch mang tnh c th v thnh phn acid amin, trt t cc acid amin trong chui.Trong t bo protein thng tn ti cc bc cu trc khng gian. Sau khi chui polypeptid - protein bc I c tng hp ti ribosome, n ri khi ribosome v hnh thnh cu trc khng gian (bc II, III, IV) ri mi di chuyn n ni s dng thc hin chc nng ca n.Cu trc bc hai: Cun gp khng gian[sa|sa m ngun]Theo Paulin v Cori (1951), c 2 kiu cu trc chnh l xon v phin gp np .- Cu trc xon ( helix): on mch polipeptide xon cht li, nhng nhm peptide (-CO-NH-), C to thnh phn bn trong (li) ca xon, cc mch bn (nhm R) ca cc gc acid amine quay ra pha ngoi. mi aa c to bi 3 nucleotit.- Cu trc xon c gi vng ch yu nh lin kt hidro. Lin kt hidro c to thnh gia cc nhm carboxyl ca 1 lin kt peptide vi nhm NH ca lin kt peptide th t sau n (cch nhau 3 gc acid amine) trn cng mt mch polipeptideTt c cc nhm CO-, -NH- trong lin kt peptide ca mch polipeptide u to thnh lin kt hidro theo cch ny.Trong cu trc xon , c mi nhm CO-NH- c th to 2 lin kt hidro vi 2 nhm CO-NH- khc. Cc lin kt hidro c to thnh vi s lng ti a, bo m bn vng ca cu trc .Theo m hnh ca Paulin v Cori, trong cu trc xon gia 2 gc acid amine k tip nhau c khong cch dc thep trc xon l 1,5AO v gc quay 100O, 1 vng xon c 3,6 gc acid amine c chiu cao tng ng l 5,4 AO.Chiu ca vng xon c th l xon phi (theo chiu thun kim ng h) hoc xon tri (ngc chiu kim ng h). Xon trong phn t protein thng l xon phi.S to thnh v bn ca cu trc xon ph thuc vo nhiu yu t, v d thnh phn v trnh t sp xp ca cc acid amine trong mch polipeptide, pH mi trng, n nay ngi ta bit c mt s quy lut c bn to thnh xon , V vy, nu xc nh c cu trc bc I ca phn t protein th c th d on t l xon (% s gc acid amine tham gia to thnh xon) v v tr ca cu trc xon trong phn t protein.T l% xon trong phn t protein khc nhau thay i kh nhiu.vi d: trong hemoglobin v mioglobin l 75%, lozozim l 35%, kimotripsin hu nh khng c xon , ch c mt phn xon rt ngn u C.Khi to thnh cu trc xon , kh nng lm quay mt phng nh sng phn cc sang bn phi tng ln, v th c th da vo tnh cht ny xc nh% xon trong phn t protein.Cu trc phin gp ( sheet)[sa|sa m ngun]Cu trc phin gp tm thy trong fiborin ca t, n khc vi xon mt s im nh sau:+on mch polipeptide c cu trc phin gp thng dui di ra ch khng cun xon cht nh xon . Khong cch gia 2 gc acid amine k nhau l 3,5AO.+Lin kt hidro c to thnh gia cc nhm NH- v CO- trn 2 mch polipeptide khc nhau, cc mch ny c th chy cng hng hay ngc hng vi nhau.Trong phn t ca nhiu protein hnh cu cun cht, cn gp kiu cu trc quay- . mch polipeptide b o hng t ngt. l do to thnh lin kt hidro gia nhm CO ca lin kt peptide th n vi nhm NH ca lin kt peptide th n+2Cu trc kiu xon colagen[sa|sa m ngun]Kiu cu trc ny tm thy trong phn t colagen. Thnh phn acid amine ca colagen rt c bit so vi cc proteein khc: glyxin 35%, prolin 12% tng s acid amine trong phn t. Ngoi ra, colagen cn cha 2 acid amine t gp trong cc acid amine khc l hydroxiproline v hydroxilizin.n v cu trc ca colagen l tropocolagen bao gm 3 mch polipeptide bn vo nhau thnh mt dy cp siu xon (v mi mch u c cu trc xon).3 mch polipeptide trong dy cp ni vi nhau bng cc lin kt hidro.Lin kt hidro c to thnh gia cc nhm NH- ca gc glyxin trn mch polipeptide vi nhm -CO- trong lin kt peptide trn mch polipeptide khc. Ngoi ra cc nhm hydroxyl ca hydroxipoline cng tham gia to thnh lin kt hydro lm tng bn ca cu trc siu xon.Ngoi cc kiu cu trc bc II trn, trong phn t ca nhiu protein hnh cu cn c cc on mch khng cu trc xon, phn v nh hoc cun ln xn.Cu trc bc ba: Lin kt disulfid (-S - S-)[sa|sa m ngun]

Molcula decistina, fruto de la condensacin de doscistenasmediante un enlace disulfuro.Cu trc bc III c gi vng nh cc cu disulfua, tng tc VanderWaals, lin kt hidro, lc ion. V vy khi ph v cc lin kt ny phn t dui ra ng thi lm thay i mt s tnh cht ca n, c bit l tnh tan v hot tnh xc tc ca n.Cu trc bc ba l dng khng gian ca cu trc bc hai, lm cho phn t protein c hnh dng gn hn trong khng gian. S thu gn nh vy gip cho phn t protein n nh trong mi trng sng. C s ca cu trc bc ba l lin kt disulfid. Lin kt c hnh thnh t hai phn t cystein nm xa nhau trn mch peptid nhng gn nhau trong cu trc khng gian do s cun li ca mch oevtid. y l lin kt ng ho tr nn rt bn vng.Cu trc bc 3 to nn trung tm hot ng ca phn ln cc loi enzym. S thay i cu trc bc ba dn n s thay i hng xc tc ca enzym hoc mt kh nng xc tc hon ton.Ngoi lin kt disulfit, cu trc bc ba cn c n nh (bn vng) nh mt s lin kt khc nh:-Lin kt hydro: lin kt ny xut hin khi gia hai nhm tch in m c nguyn t hydro.V d v cu trc bc 3 nh:Phn t insulin l mt polypeptid bao gm 51 acid amin chui A c 21 gc acid amin v chui B c 30 gc acid amin. Hai chui ni vi nhau bi 2 cu disulfid: cu th nht gia gc cystein v tr 20 ca chui A v v tr 19 ca chui B; cu th hai gia gc cystein v tr th 7 ca c 2 chui. Trong chui A cn c mt cu disulfit gia 2 gc cystein v tr th 6 v 11. Insulin l hoocmn tuyn tu tham gia iu ho hm lng ng trong mu. Khi thiu insulin, hm lng ng trong mu tng cao, dn ti hin tng bnh i ng Insulin c tc dng h ng huyt bng cch xc tin qu trnh tng hp glycogen d tr t glucose.-Lc hp dn VanderWaals: l lc ht gia hai cht hoc hai nhm ho hc nm cnh nhau khong cch 1 - 2 ln ng knh phn t.Lc lin kt ca cc nhm k nc, nhng nhm khng phn cc (- CH2; -CH3) trong vang, leucin, isoleucin, phenylalanin... Nc trong t bo y cc gc ny li vi nhau, gia chng xy ra cc lc ht tng h v to thnh cc ui k nc trong phn t protein. Do c cu trc bc ba m cc protein c c hnh th c trng v ph hp vi chc nng ca chng. cc protein chc nng nh enzym v cc khng th, protein ca h thng ng mu... thng qua cu trc bc ba m hnh thnh c cc trung tm hot ng l ni thc hin cc chc nng ca protein.Domain cu trc (Structural domain) c nghin cu t 1976, n nay ngi ta cho rng s hnh thnh domain rt ph bin cc chui peptid tng i di. Domain cu trc c th c nh ngha l nhng b phn, nhng khu vc trong mt phn t protein c cun gp trong khng gian ging nh mt phn t protein nh hon chnh v thng l nhng ni thc hin chc nng lin kt, chc nng lp rp ca phn t protein trong hot ng chc nng ca n. Trong nhiu protein domain gn lin vi chc nng kt hp c hiu v nhiu enzym c cu to t cc domain th trung tm hot ng li c b tr bin gii ca hai hay nhiu domain S thnh thnh cc domain trong phn t protein to ra kh nng tng tc linh hot gia cc i phn t, kh nng c ng, dch chuyn tng ng gia nhng b phn trong qu trnh thc hin chc nng sinh hc. - nhng protein ngun gc khc nhau, nhng c chc nng tng t th cc domain c cu trc tng i ging nhau.Cu trc bc bn: T hp cc tiu phn[sa|sa m ngun]Phn t protein c cu trc bc IV c th phn li thun nghch thnh cc tiu phn n v. Khi phn li, hot tnh sinh hc ca n b thay i hoc c th mt hon ton. Do tn ti tng tc gia cc tiu phn n v nn khi kt hp vi mt cht no d l phn t b cng ko theo nhng bin i nht nh trong cu trc khng gian ca chng.L mt trng thi t hp hnh thnh t nhiu tiu phn protein c cu trc bc ba hon chnh. Mt s protein c xu hng kt hp li vi nhau thnh nhng phc hp, thnh nhng i phn t, khng ko theo s bin i v hot tnh sinh hc.Rt nhiu trng hp protein phi t hp li mi c hot tnh sinh hc. Trong nhng trng hp ny, cu trc bc bn l iu kin hnh thnh nn tnh nng mi ca protein.V d v cu trc bc bn:- Hemoglobin (Huyt sc t) gm 4 tiu phn protein: hai tiu phn v hai tiu phn . Nu 4 tiu phn tch ri nhau th mi tiu phn khng th vn chuyn c mt phn t O2 Khi kt hp li thnh trng thi tetramer to thnh mt khi khng gian c th gn nh hnh t din th mi c kh nng kt hp v vn chuyn kh oxy. Mt phn t hemoglobin (Ht) vn chuyn c 4 phn t oxy.- Enzym glycogen phosphorylase ( c, gan) xc tc qu trnh phn gii glycogen thnh glucose.+ trng thi khng hot ng enzym ny dng "b" (dng hai dimer tch ri nhau).+ trng thi hot ng (khi c tn hiu cn ng) hai dimer t hp li thnh tetramer (dng "a"). Khi nhu cu gii phng glucose gim, tetramer li tch thnh hai dimer, enzym tr li dng khng hot ng.Tu theo protein m s lng monomer c th thay i t 2,4,6,8 l ph bin, c bit c th ln ti trn 50 monomer.S hnh thnh cu trc bc bn to iu kin cho qu trnh iu tit sinh hc thm tinh vi, chnh xc.