3 Proteins (2) - Tertiary?& Quaternary structure, Protein Folding

本章的內(nèi)容是蛋白質(zhì)，本節(jié)將繼續(xù)討論蛋白質(zhì)的高級(jí)結(jié)構(gòu)以及蛋白質(zhì)折疊。下一節(jié)將討論蛋白質(zhì)的調(diào)節(jié)與控制。如果有不太明白的或者有錯(cuò)誤的地方隨時(shí)來(lái)找UP主喔~

文集本部分的參考文獻(xiàn)Essential Cell Biology, 5th ed. Alberts, et al. 2019. 部分內(nèi)容來(lái)自khanacademy與維基百科.

封面圖：https://sites.google.com/site/fabiopietrucci/Home/research/proteinfolding

3d Tertiary & Quaternary structure, Protein Folding?

Three principles of protein folding

????Hydrophobic - towards the inside (Hydrophobic effect, non-polar gets to non-polar parts while polar gets to polar parts.)

????Non-covalent bonds pin secondary, tertiary, quaternary structures in place

????In quaternary structure, subunits have complementary shapes and charges

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The hydrophobic effect 疏水作用，在生物中非常非常重要！

????Folded conformation in aqueous environment:

????????????Hydrophobic core (non-polar side chains) - away from the water

????????????+ surface (polar / charged side chains)

????Compacts the polypeptide chain, forming a hydrophobic core

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Non-covalent bonds pin secondary, tertiary, quaternary structures in place

????????Primary: covalent, peptide bonds

????????Secondary:

????????????H-bonds between backbone polar groups (O in carboxyl and H in amino)

????????Tertiary/Quaternary:

????????????All types of non-covalent bonds between side chains, backbone groups

????????????????????Ionic bonds, dispersion force, H-bonds

????????????Also disulfide bonds which is covalent

????????????????????Outside of the cell

????????????????????Bind itself in the tertiary, and between proteins in the quaternary

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Secondary structures pack together to form tertiary structure

????????Interact via side chains between them

????????Amino acid sequence determines protein fold

The overall 3-D structure of a polypeptide is called its tertiary structure.

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Complementary shapes and charges

????????Specific to quaternary structures - proteins in a Protein Complex

????????Shape: fit “puzzle”?pieces

????????????????Tight packing, subunits fit together snugly, no open spaces

????????????????Maximized dispersion forces - help hold two protein together (fit puzzle)

Charges: ionic bonds

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Denaturation

????Unfolding - Usually needs heat

????Loss of secondary and tertiary structures

????Becomes an extended polypeptide chain

????No correct 3-D conformation, no function

3-D structure is critical for protein function - eg substrate specific binding pockets

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Cofactors

????Non-protein components, needed for protein functions

????Have chemical properties, not available with side chains alone

????Eg heme group with iron binds oxygen

?

Domains: A sub-part of a polypeptide

- Each domain

????Folds independently - has its own hydrophobic core

????Carries out a different sub-function

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One polypeptide - 1 covalently connected peptide backbone - can be a two-domain protein (two hydrophobic cores)

Two polypeptide - no covalent connection - can be a two-subunit protein complex (two hydrophobic cores)

????No covalent connection between red & blue subunits. There are two domains in each subunit: top - binding DNA; bottom - binding lactose

????Be careful: 2 subunits 1 domain each looks similar as 1 subunit 2 domains each

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Unfolded proteins (exposed to water) tend to aggregate

????Exposed hydrophobic regions stick together

????Multiple proteins end up in a tangled mass

Chaperone - proteins that help other proteins to fold.

????Protect hydrophobic surfaces from water before the protein is properly folded

????Prevent unwanted hydrophobic interactions - Do not determine specific structure