Cov qauv tertiary ntawm cov protein yog txoj hauv kev uas cov saw hlau polypeptide tau muab ntim rau hauv qhov chaw peb sab. Qhov no conformation tshwm sim vim yog tsim cov tshuaj bonds ntawm amino acid radicals tej thaj chaw deb ntawm ib leeg. Cov txheej txheem no yog ua tiav nrog kev koom tes ntawm cov txheej txheem molecular ntawm tes thiab ua lub luag haujlwm loj hauv kev muab cov protein ua haujlwm ua haujlwm.
Txoj kev ntawm cov qauv tertiary
Cov tshuaj lom neeg hauv qab no yog cov yam ntxwv ntawm cov qauv tertiary ntawm cov protein:
- ionic;
- hydrogen;
- hydrophobic;
- van der Waals;
Ydisulfide.
Tag nrho cov ntawv cog lus no (tshwj tsis yog covalent disulfide) tsis muaj zog heev, txawm li cas los xij, vim qhov nyiaj lawv ruaj khov ntawm cov qauv ntawm cov molecule.
Qhov tseeb, qib peb ntawm folding ntawm polypeptide chains yog kev sib xyaw ntawm ntau yam ntawm cov qauv theem nrab (α-helices; β-pleated txheej thiabloops), uas yog taw qhia nyob rau hauv qhov chaw vim tshuaj lom neeg kev sib tshuam ntawm sab amino acid radicals. Txhawm rau schematically qhia cov qauv tertiary ntawm cov protein, α-helices yog qhia los ntawm lub tog raj kheej lossis cov kab kauv, folded khaubncaws sab nraud povtseg ntawm xub, thiab loops los ntawm cov kab yooj yim.
Qhov xwm txheej ntawm tertiary conformation yog txiav txim los ntawm qhov sib lawv liag ntawm cov amino acids nyob rau hauv cov saw, yog li ob molecules nrog tib lub ntsiab qauv nyob rau hauv vaj huam sib luag tej yam kev mob yuav sib haum mus rau tib lub variant ntawm spatial packing. Qhov kev sib haum xeeb no ua kom cov haujlwm ua haujlwm ntawm cov protein thiab hu ua haiv neeg.
Thaum lub sijhawm folding ntawm cov protein molecule, cov khoom ntawm lub chaw ua haujlwm los ze zog ua ke, uas nyob rau hauv thawj cov qauv tuaj yeem raug tshem tawm ntawm ib leeg.
Rau ib leeg-stranded proteins, cov qauv tertiary yog daim ntawv ua haujlwm kawg. Complex multi-subunit proteins tsim ib tug quaternary qauv uas characterizes kev npaj ntawm ob peb chains nyob rau hauv kev sib raug zoo rau ib leeg.
Tus yam ntxwv ntawm cov tshuaj tiv thaiv hauv cov qauv tertiary ntawm cov protein
Rau qhov loj, qhov folding ntawm cov saw hlau polypeptide yog vim qhov sib piv ntawm hydrophilic thiab hydrophobic radicals. Cov yav dhau los zoo li cuam tshuam nrog hydrogen (ib qho tseem ceeb ntawm cov dej) thiab yog li ntawd nyob rau saum npoo, thaum thaj chaw hydrophobic, ntawm qhov tsis sib xws, maj mus rau qhov chaw ntawm cov molecule. Qhov kev sib haum xeeb no yog qhov muaj zog tshaj plaws. ATqhov tshwm sim yog lub globule nrog ib tug hydrophobic core.
Hydrophilic radicals, uas txawm li cas los xij poob rau hauv nruab nrab ntawm cov molecule, cuam tshuam nrog ib leeg los tsim cov ionic lossis hydrogen bonds. Ionic bonds tuaj yeem tshwm sim ntawm qhov sib txawv ntawm cov amino acid radicals, uas yog:
- pawg cationic ntawm arginine, lysine lossis histidine (muaj qhov zoo);
- Carboxyl pawg ntawm glutamic thiab aspartic acid radicals (muaj tus nqi tsis zoo).
Hydrogen bonds yog tsim los ntawm kev sib cuam tshuam ntawm uncharged (OH, SH, CONH 2) thiab them hydrophilic pawg. Covalent daim ntawv cog lus (qhov muaj zog tshaj plaws nyob rau hauv tertiary conformation) tshwm sim ntawm SH pawg ntawm cysteine residues, tsim cov kev sib txuas hu ua disulfide. Feem ntau, cov pab pawg no tau sib nrug nyob rau hauv ib txoj kab ncaj nraim thiab mus rau ib leeg tsuas yog thaum txheej txheem stacking. Disulfide bonds tsis yog tus yam ntxwv ntawm feem ntau cov proteins hauv cellular.
Kev sib haum xeeb
Vim tias cov ntawv cog lus uas tsim cov qauv tertiary ntawm cov protein muaj zog heev, Brownian kev txav ntawm atoms hauv cov saw hlau amino acid tuaj yeem ua rau lawv tawg thiab tsim nyob rau hauv qhov chaw tshiab. Qhov no ua rau muaj kev hloov pauv me ntsis hauv cov duab spatial ntawm tus kheej ntu ntawm cov molecule, tab sis tsis ua txhaum cov haiv neeg ntawm cov protein. Qhov tshwm sim no hu ua conformational lability. Qhov kawg ua lub luag haujlwm loj hauv lub cev ntawm cov txheej txheem ntawm tes.
Protein conformation yog cuam tshuam los ntawm nws kev cuam tshuam nrog lwm tusmolecules los yog hloov nyob rau hauv lub cev thiab tshuaj parameters ntawm nruab nrab.
Yuav ua li cas cov qauv tertiary ntawm cov protein tsim
Cov txheej txheem ntawm folding ib qho protein rau hauv nws hom ntawv yog hu ua folding. Qhov tshwm sim no yog ua raws li qhov xav tau ntawm cov molecule los txais yuav kev sib haum xeeb nrog tus nqi tsawg kawg nkaus ntawm lub zog dawb.
Tsis muaj protein ntau xav tau cov kws qhia nruab nrab uas yuav txiav txim siab txog qib theem. Cov qauv nteg yog pib "sau" hauv cov kab ke ntawm cov amino acids.
Txawm li cas los xij, nyob rau hauv ib txwm muaj, txhawm rau kom muaj cov protein ntau molecule los txais yuav ib txwm ua raws li cov qauv qauv, nws yuav siv sijhawm ntau tshaj li ib lab lab xyoo. Txawm li cas los xij, hauv ib lub cell uas muaj sia nyob, cov txheej txheem no tsuas yog ob peb kaum feeb xwb. Qhov kev txo qis hauv lub sijhawm yog muab los ntawm kev koom tes hauv folding tshwj xeeb cov proteins - foldases thiab chaperones.
Qhov folding ntawm me me protein molecules (txog 100 amino acids nyob rau hauv ib tug saw) tshwm sim sai heev thiab tsis muaj kev koom tes ntawm intermediaries, uas tau pom los ntawm hauv vitro thwmsim.
Folding factor
Cov proteins uas koom nrog hauv folding tau muab faib ua ob pawg:
- foldases - muaj kev ua haujlwm catalytic, yuav tsum muaj qhov qis qis dua rau qhov concentration ntawm cov substrate (zoo li lwm cov enzymes);
- chaperones - cov proteins uas muaj ntau yam kev ua haujlwm ntawm kev ua haujlwm, xav tau nyob rau hauv ib qho kev sib piv piv rau cov nyiaj folded substrate.
Ob hom kev koom nrog hauv kev sib tw, tab sis tsis suav nrogkhoom kawg.
Pab pawg ntawm foldases yog sawv cev los ntawm 2 enzymes:
- Protein disulfide isomerase (PDI) - tswj qhov tsim nyog ntawm disulfide bonds hauv cov proteins nrog ntau cov cysteine residues. Qhov kev ua haujlwm no tseem ceeb heev, txij li kev sib cuam tshuam covalent muaj zog heev, thiab thaum muaj kev sib txuas tsis raug, cov protein yuav tsis tuaj yeem rov kho nws tus kheej thiab ua raws li haiv neeg.
- Peptidyl-prolyl-cis-trans-isomerase - muab kev hloov pauv hauv kev teeb tsa ntawm cov radicals nyob rau ntawm ob sab ntawm proline, uas hloov cov xwm txheej ntawm khoov ntawm cov saw hlau polypeptide hauv cheeb tsam no.
Yog li, foldases ua lub luag haujlwm kho hauv kev tsim cov tertiary conformation ntawm cov protein molecule.
Nyob zoo ib tsoom niam txiv kwv tij neej tsas sawv daws
Chaperones yog lwm yam hu ua kev poob siab lossis kev ntxhov siab proteins. Qhov no yog vim muaj qhov nce ntxiv hauv lawv cov zais cia thaum muaj kev cuam tshuam tsis zoo rau ntawm tes (kub, hluav taws xob, hlau hnyav, thiab lwm yam).
Chaperones muaj peb tsev neeg protein: hsp60, hsp70 thiab hsp90. Cov proteins no ua haujlwm ntau yam, suav nrog:
- Kev tiv thaiv cov proteins los ntawm denaturation;
- tsis suav nrog kev sib cuam tshuam ntawm cov proteins uas tau tsim tawm tshiab nrog ib leeg;
- tiv thaiv kev tsim cov kev sib cog lus tsis muaj zog ntawm cov radicals thiab lawv cov labialization (kev kho).
Yog li, cov neeg ua haujlwm pab txhawb kom tau txais txiaj ntsig sai ntawm kev ua kom muaj zog kom raug, tsis suav nrog kev suav sau ntau yam kev xaiv thiab tiv thaiv tsis tau siav.protein molecules los ntawm kev sib cuam tshuam tsis tsim nyog rau ib leeg. Tsis tas li ntawd, cov thawj coj muab:
- qee hom kev thauj khoom protein;
- refolding tswj (kev kho dua tshiab ntawm cov qauv tertiary tom qab nws poob);
- tuav lub xeev folding tsis tiav (rau qee cov proteins).
Nyob rau tom kawg, chaperone molecule tseem khi rau cov protein thaum kawg ntawm txoj kev folding.
Denaturation
Kev ua txhaum ntawm tertiary qauv ntawm cov protein nyob rau hauv kev cuam tshuam ntawm txhua yam yog hu ua denaturation. Qhov poob ntawm haiv neeg conformation tshwm sim thaum muaj coob tus tsis muaj zog bonds stabilize lub molecule yog tawg. Hauv qhov no, cov protein poob nws cov haujlwm tshwj xeeb, tab sis khaws nws cov qauv tseem ceeb (peptide daim ntawv cog lus tsis raug rhuav tshem thaum lub sijhawm denaturation).
Thaum lub sijhawm denaturation, qhov nce ntawm cov protein molecule tshwm sim, thiab thaj chaw hydrophobic rov los rau saum npoo. Cov saw hlau polypeptide tau txais qhov sib txawv ntawm qhov sib txawv ntawm qhov sib txawv, cov duab uas nyob ntawm seb cov ntawv cog lus ntawm cov protein cov qauv tertiary tau tawg lawm. Nyob rau hauv daim ntawv no, lub molecule yog ntau raug rau cov teebmeem ntawm proteolytic enzymes.
yam ua txhaum txoj cai tertiary
Muaj ntau lub cev thiab tshuaj lom neeg uas tuaj yeem ua rau denaturation. Cov no suav nrog:
- kub siab tshaj 50 degrees;
- hluav taws xob;
- hloov pH ntawm nruab nrab;
- hnyav hlau ntsev;
- qee cov organic tebchaw;
- tshuaj ntxuav tes.
Tom qab qhov kev txiav tawm ntawm cov nyhuv denaturing, cov protein tuaj yeem kho cov qauv tertiary. Cov txheej txheem no hu ua renaturation lossis refolding. Nyob rau hauv vitro tej yam kev mob, qhov no tsuas yog ua tau rau cov protein me me. Nyob rau hauv ib lub cell nyob, refolding yog muab los ntawm chaperones.
