Signalling through Ubiquitin Ligase

Made by-Akum Paul Singh

Roll No.2084

What happens during Stress?

An external factor that exerts a disadvantageous influence on plant  Protein damage is a key event in the stress condition protein damage can be highly toxic causes the loss of function of that specific molecule  the improper exposure of hydrophobic amino acid side chains, lead

to the aggregation of other proteins.

How plants face protein degradation problem?

inducing the transcription of a set of genes whose products, known as stress proteins, enhance survival under stress conditions

 Levels of damaged proteins can be reduced in two ways 

On the one hand, specific molecular chaperones can prevent the aggregation of damaged proteins, and catalyze their refolding

On the other hand, specific proteases can degrade damaged proteins

Scientist who discovered ubiquitin mediated proteolysis

Avram Hershko Aaron Ciechanover Irwin Rose

Nobel prize in chemistry, 2004

Ubiquitin Consists of 76 amino

acids, 8.5 kDa Found in all

eukaryotic cells (ubiquitously)

Highly Conserved Used in post-

translational modification

Small protein with big function

small, heat-stable, compact globular protein (76 AA)

Found only in eukaryotic organisms Highly conserved

Ubiquitin Genes

UBA52 RPS27A UBB UBC

Primary structure Met1-Gln2-Ile3-Phe4-Val5-Lys6-Thr7-Leu8-Thr9-Gly10-Lys11-

Thr12-Ile13-Thr14-Leu15-Glu16-Val17-Glu18-Pro19-Ser20-Asp21-Thr22-Ile23-

Glu24-Asn25-Val26-Lys27-Ala28-Lys29-Ile30-Gln31-Asp32-Lys33-Glu34-Gly35-Ile36-Pro37-Pro38-Asp39-Gln40-Gln41-Arg42-Leu43-Ile44-Phe45-

Ala46-Gly47-Lys48-Gln49-Leu50-Glu51-Asp52-Gly53-Arg54-Thr55-Leu56-

Ser57-Asp58-Tyr59-Asn60-Ile61-Gln62-Lys63-Glu64-Ser65-Thr66-Leu67-His68-Leu69-Val70-Leu71-Arg72-Leu73-Arg74-Gly75-Gly76

Three types of Ubiquitination

MonoubiquitinationAdds one ubiquitin molecule to one

substrate protein residueRequired before a poly chain can begin to

formMembrane Trafficking, Transcription,

Endocytosis

PolyubiquitinationRequires one Ub linked to substrate before

chain begins to form.Chains made by linking Glysine residue of

Ub to a Lysine of a Ub bound to a substrate.

Linking to different position on Ub leads to different results.

Lysine 48-linked polyubiquitinationLinked by 48th amino

acid (Lysine)Marks proteins for

destructionRequires at least 4 Ub to

be recognized by proteasome

E3 ligasesThe most varied of the three enzymes.Each E3 can attach to many different substrate proteins. Different E2, E3 pairings will recognize different

proteins by distinct degradation signals.

26S Proteasome Abundant in nucleus

and cytoplasm destroys proteins

marked by Ubiquitin through Lysine 48-linked polyubiquitination

26S Proteasome Consists of central

hollow cylinder (20S) 4 stacked “rings” of 7

proteins each Capped by regulatory

particles (19S) that recognize ubiquitin through ubiquitin binding domains (UBDs)

Ubiquitin in Protein Degradation

Deubiquitinating enzyme (DUB) Around 100 in the

human genome Some cleave the whole

chain, some only cleave a set amount of Ubs

DUB USP5 selectively binds a 4-ubiquitin chain and severs it.

Regulation of Protein Degradation

One means of controlling Ubiquitination is regulating the activation of E3 ligases.