5i7j | pdb_00005i7j
Crystal Structure of Human SPLUNC1 Disulfide Mutant M3 (I76C, V214C)
Structural highlights
Function[BPIA1_HUMAN] May be involved in the airway inflammatory response after exposure to irritants. May be associated with tumor progression. May play a role in innate immune responses of the upper airways.[1] Publication Abstract from PubMedSPLUNC1 is an abundantly secreted innate immune protein in the mammalian respiratory tract that exerts bacteriostatic and antibiofilm effects, binds to lipopolysaccharide (LPS), and acts as a fluid-spreading surfactant. Here, we unravel the structural elements essential for the surfactant and antimicrobial functions of human SPLUNC1 (short palate lung nasal epithelial clone 1). A unique alpha-helix (alpha4) that extends from the body of SPLUNC1 is required for the bacteriostatic, surfactant, and LPS binding activities of this protein. Indeed, we find that mutation of just four leucine residues within this helical motif to alanine is sufficient to significantly inhibit the fluid spreading abilities of SPLUNC1, as well as its bacteriostatic actions against Gram-negative pathogens Burkholderia cenocepacia and Pseudomonas aeruginosa. Conformational flexibility in the body of SPLUNC1 is also involved in the bacteriostatic, surfactant, and LPS binding functions of the protein as revealed by disulfide mutants introduced into SPLUNC1. In addition, SPLUNC1 exerts antibiofilm effects against Gram-negative bacteria, although alpha4 is not involved in this activity. Interestingly, though, the introduction of surface electrostatic mutations away from alpha4 based on the unique dolphin SPLUNC1 sequence, and confirmed by crystal structure, is shown to impart antibiofilm activity against Staphylococcus aureus, the first SPLUNC1-dependent effect against a Gram-positive bacterium reported to date. Together, these data pinpoint SPLUNC1 structural motifs required for the antimicrobial and surfactant actions of this protective human protein. Structural Features Essential to the Antimicrobial Functions of Human SPLUNC1.,Walton WG, Ahmad S, Little MS, Kim CS, Tyrrell J, Lin Q, Di YP, Tarran R, Redinbo MR Biochemistry. 2016 May 31;55(21):2979-91. doi: 10.1021/acs.biochem.6b00271. Epub , 2016 May 17. PMID:27145151[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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