Molecular complexity of the major urinary protein system of the Norway rat, Rattus norvegicus

Area of Science:

• Rodent chemical communication
• Proteomics
• Molecular biology

Background:

• Major Urinary Proteins (MUPs) are key urinary proteins in rodents, crucial for semiochemical communication.
• While well-studied in mice, MUPs in Norway rats (Rattus norvegicus) lack detailed characterization regarding isoforms and functions.
• Understanding rat MUPs is essential to explore potential differences in rodent chemical communication.

Purpose of the Study:

• To conduct a detailed molecular characterization of MUP proteoforms in Norway rat urine.
• To compare the complexity of MUP primary sequences and post-translational modifications between rats and mice.
• To investigate the implications of these findings for the functional roles of MUPs in rat chemical communication.

Main Methods:

• Manual gene annotation and cluster analysis to identify mup gene numbers.
• Intact protein mass spectrometry and bottom-up mass spectrometry-based proteomics for MUP isoform sequencing.
• Analysis of post-translational modifications, including phosphorylation and proteolytic trimming.

Main Results:

• Identified only 10 predicted mup genes in Norway rats, indicating less primary sequence polymorphism than in mice.
• Discovered significant post-translational modifications in rat MUPs, such as Ser4 phosphorylation and exoproteolytic trimming.
• Revealed a distinct pattern of MUP complexity in rats, differing from that observed in mice.

Conclusions:

• Rat MUPs exhibit a unique combination of limited primary sequence variation and complex post-translational modifications.
• These molecular characteristics suggest that rat MUPs may serve different functions in chemical communication compared to mouse MUPs.
• Further research is needed to elucidate the specific roles of these modified rat MUPs in rodent social interactions.