1.C.40 The Bactericidal Permeability-Increasing Protein (BPIP) Family
The BPI protein is produced within the granules of neutrophiles (polymorphonuclear leukocytes) of mammals. They have bacteriocidal activity against many species of Gram-negative bacteria. The cationic N-terminal half of the protein has high affinity for the anionic LPS-containing outer membranes of these bacteria. BPIP can neutralize the toxic effects of LPS in humans.
The structure of BPIP's reveals a novel protein fold with two similar domains that give the protein two-fold symmetry. Two phospholipids are bound in a polar pocket of the protein.
While BPIP and lipopolysaccharide binding protein (LBP) are concerned with host responses to bacterial infections and LPS, respectively, other homologues such as CETP and PLTP (see below) and other lipid transport proteins regulate the sizes of LDL and HDL in the plasma of mammals. This family is called the BPI/LBP by SwissProt.