A localized multimeric anchor attaches the Caulobacter holdfast to the cell pole.
Caulobacter crescentus attachment is mediated by the holdfast, a complex of polysaccharide anchored to the cell by HfaA, HfaB and HfaD. We show that all three proteins are surface exposed outer membrane (OM) proteins. HfaA is similar to fimbrial proteins and assembles into a high molecular weight (HMW) form requiring HfaD, but not holdfast polysaccharide. The HfaD HMW form is dependent on HfaA but not on holdfast polysaccharide. We show that HfaA and HfaD form homomultimers and that they require HfaB for stability and OM translocation. All three proteins localize to the late pre-divisional flagellar pole, remain at this pole in swarmer cells, and localize at the stalk tip after the stalk is synthesized at the same pole. Hfa protein localization requires the holdfast polysaccharide secretion proteins and the polar localization factor PodJ. An hfaB mutant is much more severely deficient in adherence and holdfast attachment than hfaA and hfaD mutants. An hfaA, hfaD double mutant phenocopies either single mutant, suggesting that HfaB is involved in holdfast attachment beyond secretion of HfaA and HfaD. We hypothesize that HfaB secretes HfaA and HfaD across the outer membrane, and the three proteins form a complex anchoring the holdfast to the stalk.
Department of Biology, Jordan Hall 142, Indiana University, 1001 E. 3rd Street, Bloomington, IN 47405, USA.
Gail G
GG
Hardy
Rebecca C
RC
Allen
Evelyn
E
Toh
Maria
M
Long
Pamela J B
PJ
Brown
Jennifer L
JL
Cole-Tobian
Yves V
YV
Brun
D018829:Adhesins, Bacterial / Q000378:metabolism; D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D016935:Caulobacter crescentus / Q000472:pathogenicity / Q000502:physiology*; D005407:Flagella / Q000737:chemistry; D054884:Host-Pathogen Interactions; D046911:Macromolecular Substances / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D037521:Virulence Factors / Q000378:metabolism*
D018829:Adhesins, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C117825:HfaA protein, Caulobacter crescentus; C086643:HfaD protein, Caulobacter crescentus; D046911:Macromolecular Substances; D008565:Membrane Proteins; D011134:Polysaccharides; D037521:Virulence Factors