Bellizzi biochimica lecture10 fibrous proteins, folding, and denaturing

globular protein chains fold up into

relatively compact, quasi spherical shapes

different segments of secondary structure are interspersed with turns and loops associate to form tertiary structure in

globular protein

fibrous proteins are large extended molecules of

relatively simple and uniform structure(rods/sheets)

fibrous proteins consist of a single type of

secondary structure

fibrous proteins are what in water

insoluble

where are fibrous proteins located

extracellular

important examples of fibrous proteins

alpha keratin, fibroin, collagen

alpha keratin is composed of

all alpha helical, in hair, fingernails, claws, horns, hooves

fibroin consists of

all beta sheets, in silk

collagen consist of

collagen triple helix, in tendons, cartilage, skin, cornea, intervertebral disk.

fibrous proteins have no

tertiary structure

fibrous proteins found in all

higher vertebrates

mammals have more than

50 different keratin peptides

keratin is a homodimer of

two alpha helical polypeptide chains wrapped around each other to form a left handed superhelix

heptad repeat

consists of a repeating pattern of 7 amino acids: abcdefg

in a heptad repeat a and d are

hydrophobic (often Leu)

a heptad repeat creates

a hydrophobic "strip" that is buried when two helices form coiled coil

higher order assembly of ketatin

helices intertwine to form coiled coils

-coiled coils bundle into protfilaments

-protofilaments bundle into protofibrils

disulfide bonds form between coiled coils and

adjacent coiled coils- insoluble and resistant to stretching

hard keratins

more Cys, less pliable

soft keratins

less Cystic, more pliable

collagen is a

triple helical cable

most abundant protein in vertebrates

collagen

collagen is extracellular and made of

insoluble fibers of great tensile strength

major stress bearing cable of connective tissue

collagen

collagen makes up

skin, bone, tendon, blood vessels, cornea

collagen is a ________ triple helix

type1

collagen primary structure length

abound 1000 residues long

most common residues in collagen

Gly and Pro

primary structure contains a significant amount of

4-hydroxyproline and 3-hydroxyproline and 5-hydroxylysine

unique secondary structure of collagen helix

left handed helix with 3 residues per turn

unique secondary structure of collagen helix formed from

repeating units of Gly-X-Y

X Is usually

Pro

Y is usually

4-Hyp

what is important for structure and stability of collagen

hydrated Pro and Lys

what hydroxylates Pro to 4-Hyp at point Y of G-X-Y

prolyl hydroxylase

what kind of bonds does 4-Hyp form

intramolecular H bonds

what does collagen without 4-Hyp do?

denatures at a lower temperature than normal collagen

gelatin

denatured collagen

Lysol oxidase converts

Lys to 5-hydroxylysine

Hyl can form intramolecular covalent crosslinks with

other Lys to His side chains

there are no disulfide links in collagen because there is

very little Cys

prolyl hydroxylase has a catalytic

Fe2+ ion

fibroin is a heterotrimer of

fibroin heavy chain, fibroin light chain, and P25 glycoprotein

fibroin heavy chain is highly enriched with

Ala, Gly with long polyAla stretches, and Gly-Gly-X stretches

fibroin facilitates the formation of

antiparallel beta sheets that can pack tightly together for maximum dispersion forces

one of the strongest biopolymers

silk

silk has high strength and

flexibility

proteins are not rigid but

flexible

proteins are undergoing low amplitude

fluctuation around native conformation

biological activity requires

protein to be properly folded

denatured/ unfolded state

structure is disrupted to the point that biological activity is lost

denatured state is

higher in free energy

in the denatured state, the primary structure is

not disrupted

complete denaturation often requires reduction of

disulfide links

a protein is in equilibrium between

native and denatured state

under normal cellular conditions, equilibrium,ibrium strongly favors

native state

things that favor denatured state

heat, pH extremes, organic solvents, detergents, chaotropes

under physiological conditions delta G for folding is

less than zero

what kind of processes are folding and denaturation

cooperative

Tm

temperature at which 50% of molecules are folded and 50% are unfolded

folding/ denaturation is a

reversible process

a denatured protein can do what when denaturing conditions re removed

spontaneously refold

all information for adopting native fold is located in

amino acid sequence

ribonuclease A adds 8M urea an beta mercaptoethanol leading to

protein activity loss

chemically synthesized RNAseA folds

spontaneously into native conformation

amino acid sequence leads to a limited number of

favorable folding pathways

proteins fold in an ordered pathway ir set of pathways in which approach to the native state is

accompanied by dramatic increase in conformation stability

secondary structure forms as protein is

synthesized

individual helices and strands form _______ in different parts of the chain

independently and simultaneously

after secondary structure forms what occurs

longer range associations

motifs form from

helices and strands

domains form from

motifs

long range associations driven by

hydrophobic effect

free energy funnel for protein folding

cellular proteosome

entire set of proteins produced at a given time in a given cell under given conditions

proteostasis

dynamic regulation f a functional cellular proteasome

proteins are synthesized on

ribosomes

newly synthesized proteins fold rapidly and spontaneously into their

tertiary structures

chaperone proteins assist by sequestering

misfiled, partially folded, or aggregated proteins and giving them a chance to refold

when a protein is no longer needed it can be tagged fo destruction by

ubiquitin and transferred to proteasome

misfiled proteins are

tagged for degradation

aggregated proteins can form

insoluble deposits that can cause various pathologies

misfiled/denatured proteins will aggregate due to

the hydrophobic effect

molecular chaperones

proteins that assist in protein folding, rescue unfolded proteins, disrupt nonfunctional protein aggregates

two main families (both ATP dependant)

heat shock proteins and chapheronins

common features of both families of chaperones

undergo conformational changes, bind APT and hydrolyze ig to ADP+Pi

folding accessory proteins

isomerase enzymes

isomerase enzymes assist folding of certain proteins when they

get "stuck"

protein disulfide isomerase

catalyzes disulfide bond shuffling

peptide propel cis-trans isomerase

interconverts trans/ cis prolines

up to 30 percent of cellular proteins need to be either refolded or degraded to prevent accumulation of

misfiled, nonfunctional protein

misfiled protein aggregates can impair function of

normal proteins

some protein folding diseases cause degradation of misfiled proteins rather than aggregation, and symptoms arise from

lack of degraded protein

amyloidoses

misfiled/ partially folded secreted proteins associate via beta sheets to form long amyloid fibril

insoluble amyloid fibrils accumulate in affected tissue and cause

cell damage/death

prion diseases

transmissible spongiform encephalopathies

prions

protein infectious particles

a misfiled protein (prion) catalyzes the conversion of normal cellular protein to a

misfiled protein that aggregates