Category: Lab Notes: Immunology

Peptides are short chains of amino acids that act as essential messengers, regulators, and structural molecules in living organisms. This article explores how peptides are formed, how they function, and why they are vital in biology and modern medicine.

TRIM5α is a specialised antiviral ubiquitin ligase that recognises retroviral capsids, assembles K63‑linked ubiquitin chains and promotes autophagic degradation. Its tripartite motif and SPRY domain enable potent restriction of retroviruses, making TRIM5α a key factor in innate antiviral immunity and retroviral defence.

RIG‑I is a cytosolic pattern‑recognition receptor that detects viral RNA and activates innate immunity. Its CARD domains become exposed and ubiquitinated by TRIM25, enabling RIG‑I to bind MAVS and trigger interferon production. Through this pathway, RIG‑I converts viral RNA detection into a strong antiviral response.

MDA5 is a cytosolic receptor that detects long viral double‑stranded RNA and activates MAVS‑dependent interferon signalling. Its ATP‑driven filament formation enables precise recognition of replicating RNA viruses, while LGP2 stabilises MDA5 filaments to ensure accurate antiviral responses.

TRIM21 is a unique intracellular antibody receptor and RING finger ubiquitin ligase that neutralises antibody‑coated viruses inside the cytosol. Through its PRY/SPRY domain and tripartite motif, TRIM21 triggers rapid ubiquitin‑mediated degradation and activates antiviral signalling pathways. Its roles in immunity, autoimmunity and biotechnology make TRIM21 a key regulator of intracellular defence.

TRIM25 is a RING finger ubiquitin ligase that activates the antiviral sensor RIG‑I through K63‑linked ubiquitination. Its tripartite motif and PRY/SPRY domain enable precise regulation of innate immune signalling, interferon production and viral restriction. TRIM25 is targeted by multiple viruses, highlighting its importance as a frontline antiviral factor.

The TRIM family is a large group of single‑chain RING finger ubiquitin ligases that regulate innate immunity, antiviral defence, autophagy, transcription and protein quality control. Defined by their tripartite motif—RING, B‑box and coiled‑coil domains—TRIM proteins use diverse C‑terminal regions to achieve precise substrate specificity. Their roles in immunity, development and cancer make them key regulators of cellular homeostasis.