Co-translational processing and intracellular transport of rat salivary mucus glycoprotein

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Mucin synthesis involves complex post-translational modifications.
• Understanding the timing and location of these modifications is crucial.
• Peptidyl-tRNA plays a role in protein synthesis and modification.

Purpose of the Study:

• To investigate the co-translational nature of fatty acylation and O-glycosylation in mucin synthesis.
• To determine the specific stages of peptide synthesis where these modifications occur.
• To characterize the peptidyl-tRNA fractions involved in these processes.

Main Methods:

• Preparation and analysis of peptidyl-tRNA from sublingual salivary gland microsomes.
• Radioscanning and chemical analyses using radiolabeled methionine, palmitic acid, and N-acetylgalactosamine.
• SDS-polyacrylamide gel electrophoresis to determine peptide sizes.
• Pulse-chase experiments to track molecular events over time.

Main Results:

• Fatty acylation (palmitoylation) occurs on nascent peptides longer than 20 amino acids.
• N-acetylgalactosamine O-glycosylation is detected on galactosamine-free peptides up to 70 amino acids.
• Both N-terminal fatty acylation and O-glycosylation are confirmed as co-translational events.

Conclusions:

• Fatty acylation and O-glycosylation initiate co-translationally as peptides emerge from the ribosome.
• These modifications occur on nascent peptides within the endoplasmic reticulum lumen.
• The findings provide insights into the early stages of mucin biosynthesis.