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#nascent protein

2 public questions tagged with this topic.

Protein Sorting and Trafficking

Which domain of SRP binds to signal sequences on nascent proteins?

Specificity of signal recognition particle for hydrophobic targeting signals resides within C-terminal M domain of 54 kilodalton subunit SRP54. Structural analyses of bacterial homolog Ffh and mammalian SRP54 show M domain folds into deep groove lined almost exclusively with methionine side chains whose flexible thioether and long aliphatic chain create plastic hydrophobic bristle adaptable to varied signal sequence compositions and lengths. Basic residues surrounding groove interact with phosphate backbone of 7SL RNA and ribosomal proteins L23 and L29 near peptide exit tunnel. Adjacent NG GTP

Ref: Keenan et al., Annu Rev Biochem 70: 2001, SRP54 M Domain Binds Signal Sequences.

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Protein Sorting and Trafficking

The signal sequence of a nascent protein is cleaved by:

N-terminal signal peptides exhibit tripartite organization essential for targeting and cleavage: positively charged n-region with one to three basic residues, hydrophobic core h-region of seven to twelve aliphatic residues forming alpha-helix, and polar c-region containing signal peptidase recognition motif Ala-X-Ala at positions minus three and minus one relative to cleavage site, often followed by small residues. Once nascent chain enters ER lumen through Sec61 channel, signal peptidase complex anchored on lumenal face performs co-translational cleavage. Heteromeric complex includes two cata

Ref: Paetzel et al., Chem Rev 102: 2002, Signal Peptidase Cleaving Signal Sequences.

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