Identification and functional characterization of a novel transmembrane protein LvLRRm1 containing leucine-rich repeats in shrimp Litopenaeus vannamei.

Leucine-rich repeat (LRR) domains are evolutionarily conserved in various proteins, playing essential roles in innate immunity across vertebrates and invertebrates. In this research, we discovered and characterized a novel transmembrane protein containing an LRR domain, named LvLRRm1, in the shrimp species Litopenaeus vannamei. LvLRRm1 consists of six LRR motifs, one LRRCT motif, and a putative transmembrane domain. Phylogenetic analysis revealed that LvLRRm1 is more closely related to variable lymphocyte receptors (VLRs) than Toll-like receptors (TLRs), suggesting it may represent a distinct class of immune receptors. Functional studies showed that LvLRRm1 exhibits binding capacity for both Gram-positive and Gram-negative bacteria, with a preference for Gram-positive bacteria, and recognizes pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharides (LPS) and peptidoglycans (PGN). Knockdown of LvLRRm1 via RNA interference increased shrimp susceptibility to Vibrio parahaemolyticus infection, indicating its critical role in antibacterial immunity. Transcriptomic analysis revealed that LvLRRm1 regulates the expression of immune-related genes, including antimicrobial peptides, components of the prophenoloxidase system, and apoptosis-related factors. Additionally, LvLRRm1 may interact with the Toll3 signaling pathway, further highlighting its importance in innate immune regulation. These findings shed light on the role of LRR-containing proteins in invertebrate immunity and may present new targets for boosting disease resistance in shrimp aquaculture.