Protein Modifications-Proteomics-Lecture Slides, Slides of Proteomics

Download Protein Modifications-Proteomics-Lecture Slides and more Slides Proteomics in PDF only on Docsity!

Protein modification

• Proteins

undergo

a

variety

of

modifications

that

are

critical

for

function.

• There

are

numerous

amino

acid

modifications such as collagen.

Protein modifications -^

different types, including co-translational and post-translational

16-

Protein modification

It is estimated that the human proteome consists of~300,000 different proteins, or about 10X morethan the number of genes (!)

• protein modifications- differential splicing

docsity.com

Changes after Translation

C

hanges in the Hydrogen bond proclivity

which

results

in

secondary

and

tertiary

structures Some

of

the

proteins

might

remain

in

cytosol while others are transported acrossthe

membrane

or

even

imported

into

cellular

organelles

(mitochondria

or

chloroplasts) to accomplish their functions

Types of Post-translational

modifications

Proteolyticcleavage Glycosylation Methylation Hydroxylation Phosphorylation Sulfation

Acylation Carboxylation Prenylation Selenation Formylation Disulfide bondformation

Several types of PTMs characterized. Some of them:

Posttranslational Modifications

at the Amino-Terminus

• ~50% eukaryotic protein,the N-terminus is acetylated

Posttranslational Modifications

Addition of Prosthetic Groups

Protein Glycosylation

•^

Which proteins are decorated with glycans(polysaccharides)?

-^

What are the structures of these glycans?

-^

What is their functional significance?

Protein GlycosylationCommon in Eukaryotic Proteins

N-Linked Glycans

•^

N-linked glycans are covalently attached to Asnresidues within a consensus sequence (Asn-Xaa-Ser/Thr), enabling prediction of the modificationsites by protein sequence analysis

-^

All

N-linked

glycans

share

a^

common

pentasaccharide

core

(GlcNAc2Man3)

recognized

by lectins and N-glycanase enzymes (PNGase F)

-^

These reagents have been used to visualize proteinsbearing N-linked glycans from cell or tissue lysatesand to enrich them for mass spectrometry analysis

O-Linked Glycans

-^

Comparable tools are lacking for the study of proteins bearingO-linked glycans.

-^

Mucin-type,

the

most

prevalent

O-linked

glycosylation

is

characterized by an

N

-acetylgalactosamine (GalNAc) residue -

linked to the hydroxyl group of Ser or Thr. GalNAc residue isinstalled

by

a^

family

of

24

N

-acetyl-

galactosaminyltransferases, then further elaborated by a seriesof

glycosyltransferases

to

generate

higher-order

O-linked

structures.

-^

Because of the complex biosynthetic origin, O-linked glycansare not installed at a defined consensus motif and their presencecannot be accurately predicted based on the protein's primarysequence

Glycosylation and Protein Functions

•^

HIV

evades

the

immune

system

by

evolving

a

dynamically changing shield of carbohydrates

Nature 422(2003)

•^

Complex

sulfation

patterns

present

in

glycosaminoglycans

are

crucial

to

growth

factor

activation

Trends Genet 16(20000)

•^

O-GlcNac

glycosylation

regulate

transcription

factors such as CREB

JACS 125(2003)

Protein Glycosylation -

Biological Significance

•^

Oligosaccharides may be a tissue-specific marker

-^

Carbohydrates may alter the polarity and solubility

-^

Steric interaction between protein andoligosaccharides dictates certain protein 3D structure

-^

The bulkiness and negative charge of oligosaccharidechain may protect protein from the attack byproteolytic enzymes

Lectins

carbohydrate-binding proteins

-^

Lectins read sugar code and mediate many biologicalprocesses :[1] Cell-cell recognition[2] Signaling[3] Adhesion[4] Intracellular targeting of newly synthesized

proteins

Role of oligosaccharides in recognition and adhesion