title: Acidianus, Sulfolobus and Metallosphaera surface layers: structure, composition and gene expression.
abstract: The cell walls of Sulfolobales species consist of proteinaceous S-layers assembled from two polypeptides, SlaA and SlaB. We isolated the large S-layer protein of Acidianus ambivalens and both S-layer subunits of Sulfolobus solfataricus and Metallosphaera sedula, respectively. The slaAB genes, lying adjacently in the chromosomes, are constitutively transcribed as bicistronic operons in A. ambivalens and S. solfataricus. A smaller slaA transcript appeared in Northern hybridizations of A. ambivalens RNA. PCRs experiments showed that 80-85% of the transcripts stop at an oligo-T terminator downstream of slaA while 15-20% are read through to a second terminator downstream of slaB. The bicistronic operons including promoter and terminator regions are conserved in the Sulfolobales. While no SlaA homologue is found outside the Sulfolobales, SlaB is distantly similar to S-layer proteins of other Crenarchaeota, e.g. the Staphylothermus marinus tetrabrachion. Molecular modelling suggests SlaBs to be composed of 2-3 consecutive beta sandwich domains, a coiled-coil domain of 15-17 nm in length and a C-terminal transmembrane helix. Electron microscopy shows crystalline protein arrays with triangular and hexagonal pores. We propose that the mushroom-shaped 'unit cells' of the Sulfolobales' S-layers consist of three SlaBs anchoring the complex in the membrane and six SlaAs forming the detergent-resistant outer sacculus.
authors.affiliation: Institute of Microbiology and Genetics, Technische Universität Darmstadt, Schnittspahnstrasse 10, 64287 Darmstadt, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Veith
authors.forename: Andreas
authors.initials: A
authors.lastname: Klingl
authors.forename: Behnam
authors.initials: B
authors.lastname: Zolghadr
authors.forename: Karin
authors.initials: K
authors.lastname: Lauber
authors.forename: Reinhard
authors.initials: R
authors.lastname: Mentele
authors.forename: Friedrich
authors.initials: F
authors.lastname: Lottspeich
authors.forename: Reinhard
authors.initials: R
authors.lastname: Rachel
authors.forename: Sonja-Verena
authors.initials: SV
authors.lastname: Albers
authors.forename: Arnulf
authors.initials: A
authors.lastname: Kletzin
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D019848:Gene Expression Regulation, Archaeal; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009876:Operon; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D019642:RNA, Archaeal / Q000235:genetics; D016415:Sequence Alignment; D016942:Sulfolobales / Q000235:genetics* / Q000378:metabolism; D013728:Terminator Regions, Genetic
chemical_list: D019843:Archaeal Proteins; D008562:Membrane Glycoproteins; D019642:RNA, Archaeal; C055764:S-layer proteins