Recombinant Human CL-P1/COLEC12 Protein, CF

Collectins are a family of Ca⁺⁺-dependent, C-type lectins that contain a collagenous domain and function as recognition molecules for molecular patterns found on pathogens (1 - 4). Human collectin placenta 1 (CL-P1; also known as collectin sub-family member 12 and SRCL type I [scavenger receptor with C-type lectin type I]) is a 110 kDa member of the collectin family of glycoproteins (5, 6). With two exceptions, all collectins are secreted. CL-P1 is the only collectin known to be membrane bound, while CL-L1 (collectin liver-1) is the only known cytoplasmic collectin (1). Human CL-P1 is synthesized as a 742 amino acid (aa) type II transmembrane glycoprotein that contains an N-terminal 39 aa cytoplasmic domain, a 17 aa transmembrane segment, and a 686 aa C-terminal extracellular region (6). The short cytoplasmic domain contains an internalization motif (Y-K-R-F) while the extracellular region is complex, demonstrating a coiled-coil segment, a Ser-Thr rich region, a collagen-like structure and a C-type lectin/ carbohydrate recognition domain (CRD). Notably, this CRD recognizes galactose (and fucose) within the context of asialo-orosomucoids associated with the Lewis^x epitope (7, 8). CL-P1 has a 300 kDa trimeric form due to its collagen-like and coiled-coil helical domains (1, 5). There is a 97 kDa, alternate splice form of CL-P1 (SRCL type II) that shows a 120 aa truncation at the C-terminus. This effectively removes the entire CRD found on full-length CL-P1 (6). Human CL-P1 is 93% aa identical to mouse CL-P1 over the entire extracellular region, and 87% aa identical within each species CRD (5, 9). Human CL-P1 is known to be expressed in vascular endothelial cells (5). CL-P1 may play a role in bacterial recognition or as a scavenger receptor for desialylated.