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Protein Denaturation

FDSC400

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Goals

Denaturation

Balance of forces

Consequences of denaturation

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Effect of Temperature on Rate of

Enzyme Action

rate

denaturant

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Denaturation

Denaturation is a phenomenon that involves

transformation of a well-defined, folded

structure of a protein, formed underphysiological conditions, to an unfolded

state under non-physiological conditions.

Occurs suddenly and completely over a narrowrange of conditions

Slowly reversible (if at all)

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Hydrophobic InteractionsClathrate

water

Peptide chain

Increased chain entropy

Increased solvent entropy

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Chain Entropy

S=k ln W

Increased chain entropy

One native state

Many denatured states

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Other Factors

Hydrogen bonds

Electrostatic interactions

Consider how the total number and

strength of these bonds changes as aresult of denaturation

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Balance of Forces

Chain entropy

Solvent entropy

other forces

DG=DH-TDS

DG=DH-TDS

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Effect of T on Balance of Forces

Freeenergych

angefordena

turation

T

+ (oppose)

- (favor)

Chain entropy effect

Solvent entropy effect

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Thermal Denaturation

Trypsinogen 55C

Pepsinogen 60C

Lysozyme 72C

Myoglobin 79C

Soy Glycinin 92C

Oat globulin 108C

Table 11

Affected by pH, water,

solutes

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Why is Denaturation Sudden?

Concentration of denaturant or temperature

100%

0%

NativeSt

ructure

Critical value

COOPERATIVE PROCESS

Partly denatured structure is

weaker so begins to change faster

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Types of Denaturation

Temperature

Organic solvents

Surface

pH

Shear

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Reversibility?One native form

Many denatured form

Refolding is a complex

processparticularly for large

proteins or complex proteins

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Energy Surface

Changes in Conformation

Freeenergy

One native state

(true energy minimum)

Many secondary

minima amongst

denatured states

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Behavior of Denatured ProteinHydrophobic core

Hydrophilic surface

NATIVE

AGGREGATED

or other ingredient interactions

DENATURED

Unfolding forces some

hydrophobic AA to sur

Fast under non-physiological conditions

Slow under physiological conditions

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Consequences of Denaturation

Loss of enzymatic activity (death)

Destruction of toxins

Improved digestibility

Loss of solubility

Changes in texture

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Denaturation

The conversion of a biologically functionalmolecule into a non-functional form

There are many denatured states but onenative state

Proteins can regenerate to their native state

but slowly Denatured proteins have a greater tendency

to aggregate.