A protein is drawn in the following simplified diagram undergoing a set of post-

Question

A protein is drawn in the following simplified diagram undergoing a set of post-translational modifications including the addition of a chain of ubiquitin protein monomers (U) to one of its lysine side chains, a phosphate moiety (P) to its tyrosine side chain, and a lipid farnesyl (F) to its cysteine side chain. Indicate the nature of these modifications (1 to 3) in the diagram.

The protein is Unmodified 1 associated with the protein plasma membrane 2 The protein is 3 The protein is recognized by specifically an active E2. degraded E3 ligase

Explanation / Answer

Ans:The nature of modification of protein in the diagram are as follows.

1]Ubiquitylation=This class of proteins contains an N terminus called as signal sequence or signal peptide.

2]Phosphorylation=Activated ubiquitin now transfered to phosphate moiety of tyrosine residue.

3]Farnesylation=Attachment of lipid farnesyl to the cysteine side chain.

Ubiquitin protein ligases transfer the activated ubiquitin from E2 to a lysine amino group of its target protein,forming an isopeptide bond.A ubiquitinated protein is proteolytically degraded to short peptides in an ATP dependent process mediated by proteasome.

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