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Publication Abstract from PubMed

Type IV pili (T4P) are bacterial appendages composed of protein subunits, called pilins, non-covalently assembled into helical fibers. T4P are essential, in many bacterial species, for processes as diverse as twitching motility, natural competence, biofilm or microcolony formation, and host-cell adhesion. The genes encoding type IV pili are found universally in the Gram-negative, aerobic, non-flagellated, and pathogenic coccobacillus Acinetobacter baumannii, but there is considerable variation in PilA, the major protein subunit, both in amino acid sequence and glycosylation patterns. Here we report the X-tray crystal structure of PilA from AB5075, a recently-characterized, highly-virulent isolate, at 1.9A resolution and compare it to homologues from A. baumannii strains ACICU and BIDMC57, which are C-terminally-glycosylated. These structural comparisons revealed that PilA(AB5075) exhibits a distinctly electronegative surface chemistry. To understand the functional consequences of this change in surface electrostatics, we complemented a DeltapilA knockout strain with divergent pilA genes from ACICU, BIDMC57 and AB5075. The resulting transgenic strains showed differential twitching motility and biofilm formation while maintaining the ability to adhere to epithelial cells. PilA(AB5075) and PilA(ACICU), while structurally similar, promote different characteristics, favoring twitching motility and biofilm formation respectively. These results support a model in which differences in pilus electrostatics affect the equilibrium of microcolony formation, which in turn alters the balance between motility and biofilm formation in Acinetobacter.

The Structure of PilA from Acinetobacter baumannii AB5075 suggests a mechanism for functional specialization in Acinetobacter type IV pili.,Ronish LA, Lillehoj E, Fields JK, Sundberg EJ, Piepenbrink KH J Biol Chem. 2018 Nov 9. pii: RA118.005814. doi: 10.1074/jbc.RA118.005814. PMID:30413536^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.