title: Structure of the cytoplasmic domain of the flagellar secretion apparatus component FlhA from Helicobacter pylori.
abstract: Using x-ray crystallography we have determined the structure of the cytoplasmic fragment (residues 384-732) of the flagellum secretion system protein FlhA from Helicobacter pylori at 2.4-A resolution (r = 0.224; R(free) = 0.263). FlhA proteins and their type III secretion homologues contain an N-terminal integral membrane domain (residues 1-350), a linker segment, and a globular C-terminal cytoplasmic region. The tertiary structure of the cytoplasmic fragment contains a thioredoxin-like domain, an RNA recognition motif-like domain inserted within the thioredoxin-fold, a helical domain, and a C-terminal beta/alpha domain. Inter-domain contacts are extensive and the H. pylori FlhA structure appears to be in a closed conformation where the C-terminal domain closes against the RNA recognition motif-fold domain. Highly conserved surface residues in FlhA proteins are concentrated on a narrow surface strip comprising the thioredoxin-like and helical domains, possibly close to the export channel opening. The conformation of the FlhA N-terminal linker segment suggests a likely orientation for the FlhA cytoplasmic fragment relative to the membrane-embedded export pore. Comparison with the recently published structures of the Salmonella FlhA cytoplasmic fragment and its type III secretion counterpart InvA highlight a conformational change where the C-terminal beta/alpha domain in H. pylori FlhA moves 15 A relative to Salmonella FlhA. The conformational change is complex but primarily involves hinge-like movements of the helical and C-terminal domains. Interpretation of previous mutational screens suggest that the C-terminal domain of FlhA(C) plays a regulatory role in substrate class switching in flagellum export.
authors.affiliation: Department of Biochemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E5, Canada. stan.moore@usask.ca
authors.forename: Stanley A
authors.initials: SA
authors.lastname: Moore
authors.forename: Yunhua
authors.initials: Y
authors.lastname: Jia
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D003593:Cytoplasm / Q000502:physiology; D017931:DNA Primers; D004926:Escherichia coli / Q000235:genetics; D005407:Flagella / Q000502:physiology; D016480:Helicobacter pylori / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012475:Salmonella / Q000235:genetics / Q000502:physiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; C080688:FlhA protein, Bacteria; C455280:HfgA protein, Helicobacter pylori; D008565:Membrane Proteins; D010446:Peptide Fragments