Structure and biosynthesis of the signal-sequence receptor

Area of Science:

• Cell Biology
• Molecular Biology
• Protein Biochemistry

Background:

• The signal-sequence receptor (SSR) is a known component of the endoplasmic reticulum (ER) membrane.
• Nascent polypeptides interact with the SSR during translocation across the ER membrane.

Purpose of the Study:

• To elucidate the primary structure of the signal-sequence receptor (SSR).
• To understand the molecular mechanisms governing SSR insertion and function within the ER membrane.

Main Methods:

• Deduction of primary structure from cDNA clones.
• Direct protein sequencing.
• Analysis of protein charge distribution and phosphorylation.
• Immunofluorescence microscopy for ER localization confirmation.

Main Results:

• The SSR is a glycoprotein synthesized with a cleavable signal sequence.
• It possesses a single membrane-spanning segment and exhibits distinct charge distribution at its termini.
• SSR insertion into the ER membrane is dependent on the signal-recognition particle.
• The cytoplasmic tail of SSR is phosphorylatable, suggesting functional regulation.

Conclusions:

• The primary structure of SSR reveals key features for its ER membrane integration and function.
• Phosphorylation of the SSR cytoplasmic tail indicates a regulatory mechanism.
• SSR plays a critical role in protein translocation into the ER.