Molecular Cloning and Functional Analysis of Lumbricin in Urechis unicinctus

Abstract

Simple Summary Lumbricin is a well-known proline-rich antimicrobial peptide primarily characterized in terrestrial clitellates, with no prior reports in marine invertebrates. Here, we identified a novel lumbricin homolog from the marine benthic worm Urechis unicinctus. The deduced 67-amino-acid U. unicinctus lumbricin contained 10.4% proline and lacked a signal peptide, retaining the conserved N-terminal cationic patch and C-terminal motifs of the lumbricin family. Its transcripts were most abundant in the body wall and hindgut, which directly contact environmental microbes. Upon bacterial LPS (lipopolysaccharide) stimulation, lumbricin gene expression surged dramatically in a tissue- and time-dependent pattern, suggesting a potentially important role in the innate immune defense of U. unicinctus. Recombinant lumbricin displayed broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, with potent growth-inhibitory capacity. Our findings can expand the distribution scope of the lumbricin family and provide evidence supporting its potential role in the innate immune defense of marine non-clitellate annelids.