Profile-based data base scanning for animal L-type lectins and characterization of VIPL, a novel VIP36-like endoplasmic reticulum protein

Abstract

Consensus profiles were established to screen data bases for novel animal L-type lectins. The profiles were generated from linear sequence motifs of the human L-type lectin-like membrane proteins ERGIC-53, ERGL, and VIP36 and by optimal alignment of the entire carbohydrate recognition domain of these proteins. The search revealed numerous orthologous and homologous L-type lectin-like proteins in animals, protozoans, and yeast, as well as the sequence of a novel family member related to VIP36, named VIPL for VIP36-like. Sequence analysis suggests that VIPL is a ubiquitously expressed protein and appeared earlier in evolution than VIP36. The cDNA of VIPL was cloned and expressed in cell culture. VIPL is a high-mannose type I membrane glycoprotein with similar domain organization as VIP36. Unlike VIP36 and ERGIC-53 that are predominantly associated with postendoplasmic reticulum (ER) membranes and cycle in the early secretory pathway, VIPL is a non-cycling resident protein of the ER. Mutagenesis experiments indicate that ER retention of VIPL involves a RKR di-arginine signal. Overexpression of VIPL redistributed ERGIC-53 to the ER without affecting the cycling of the KDEL-receptor and the overall morphology of the early secretory pathway. The results suggest that VIPL may function as a regulator of ERGIC-53.