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Protein Denaturation FDSC400

Protein Denaturation

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Protein Denaturation

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Page 1: Protein Denaturation

Protein Denaturation

FDSC400

Page 2: Protein Denaturation

Goals

• Denaturation• Balance of forces• Consequences of denaturation

Page 3: Protein Denaturation

Effect of Temperature on Rate of Enzyme Action

rate

denaturant

Page 4: Protein Denaturation

Denaturation

• Denaturation is a phenomenon that involves transformation of a well-defined, folded structure of a protein, formed under physiological conditions, to an unfolded state under non-physiological conditions.– Occurs suddenly and completely over a narrow

range of conditions– Slowly reversible (if at all)

Page 5: Protein Denaturation

Hydrophobic Interactions““Clathrate” Clathrate” waterwater

Peptide chainPeptide chain

Increased chain entropy

Increased solvent entropy

Page 6: Protein Denaturation

Chain Entropy

S=k ln

Increased chain entropy

One native state

Many denatured states

Page 7: Protein Denaturation

Other Factors

• Hydrogen bonds• Electrostatic interactions

Consider how the total number and strength of these bonds changes as a result of denaturation

Page 8: Protein Denaturation

Balance of Forces

Chain entropy

Solvent entropy

other forces

G=H-TS

G=H-TS

Page 9: Protein Denaturation

Effect of T on Balance of Forces

Free

ene

rgy

chan

ge fo

r den

atur

atio

n

T

+ (oppose)

- (favor)Chain entropy effect

Solvent entropy effect

Page 10: Protein Denaturation

Thermal Denaturation

• Trypsinogen 55°C• Pepsinogen 60°C• Lysozyme 72°C• Myoglobin 79°C• Soy Glycinin 92°C• Oat globulin 108°C

Table 11

Affected by pH, water, solutes

Page 11: Protein Denaturation

Why is Denaturation Sudden?

Concentration of denaturant or temperature

100%

0%

Nat

ive

Stru

ctur

e

Critical value

COOPERATIVE PROCESS

Partly denatured structure is weaker so begins to change faster

Page 12: Protein Denaturation

Types of Denaturation

• Temperature• Organic solvents• Surface• pH• Shear

Page 13: Protein Denaturation

Reversibility?One native form

Many denatured forms

Refolding is a complex process – particularly for large proteins or complex proteins

Page 14: Protein Denaturation

Energy Surface

Changes in Conformation

Free

ene

rgy

One native state (true energy minimum)

Many secondary minima amongst denatured states

Page 15: Protein Denaturation

Behavior of Denatured ProteinHydrophobic core

Hydrophilic surface

NATIVE

AGGREGATEDor other ingredient interactions

DENATURED

Unfolding forces some hydrophobic AA to surface

Fast under non-physiological conditions

Slow under physiological conditions

Page 16: Protein Denaturation

Consequences of Denaturation

• Loss of enzymatic activity (death)• Destruction of toxins• Improved digestibility• Loss of solubility• Changes in texture

Page 17: Protein Denaturation

Denaturation

• The conversion of a biologically functional molecule into a non-functional form

• There are many denatured states but one native state

• Proteins can regenerate to their native state but slowly

• Denatured proteins have a greater tendency to aggregate.