Figure 1. Gene and protein structures of the human PLUNCs (Bingle and Bingle, 2000; Bingle and Craven, 2002). (A) Human PLUNC genes are located on chromosome 20. In mice, the corresponding gene cluster is on chromosome 2 (LeClair et al., 2001). (B) At least seven human PLUNC genes have been described. One system names the genes for the length of their protein products: three "short PLUNCs" (SPLUNC-1, -2, and -3; 250 amino acids) and four "long PLUNCs" (LPLUNC-1, -2, -3, and -4; 480 amino acids). Some of these sequences have also been published under other names (see Table 1). (C) The best-studied gene, SPLUNC-1 (also known as h-PLUNC, LUNX, or SPURT), has nine exons whose size and spacing are conserved in other short members of this family. A common factor is that the first exon contains a signal sequence for protein secretion. (D) PLUNC proteins have a predicted fold similar to that of bactericidal/permeability-increasing protein (BPI), shown as a ribbon diagram. Gray arrows indicate the BPI’s axis of symmetry between its barrel-shaped N and C-terminal domains. The "short" PLUNCS correspond in structure to the BPI N-terminus. "Long" PLUNCs have both the N- and C-terminal domains. Dark areas indicate regions of the peptide chain where the seven human PLUNCs diverge most from BPI (at the N-terminus and central hinge). Light areas show regions of greatest similarity between the two protein structures (in the barrel-shaped domains) (C.D. Bingle, unpublished data).