title: S-layer protein from Thermus thermophilus HB8 assembles into porin-like structures.
abstract: The cells of the extreme thermophile Thermus thermophilus are surrounded by a regular layer (S-layer) built up by a protein with an apparent molecular mass of 100 kDa (P100). From purified membrane fractions, three different class of two-dimensional crystals can be obtained by following alternative extractive procedures. One of these crystals, with p6 symmetry, clearly represents the native S-layer detected by freeze etching on whole cells, while the other two, showing p2 and p3 symmetries respectively, closely resemble aggregates of bacterial porins. We demonstrate here by limited proteolysis and Western blotting the surprising fact that the protein component of the three crystals is the P100 protein. Our biochemical data also show how this protein forms Ca(2+)-stabilized trimers in each crystal, which support the structural analysis that points to p3 units as the common structural block in all of them, and again resembles the situation found in bacterial porins.
authors.affiliation: Centro de Biología Molecular (CSIC-UAM), Universidad Autónoma de Madrid, Cantoblanco Spain.
authors.forename: J R
authors.initials: JR
authors.lastname: Castón
authors.forename: J
authors.initials: J
authors.lastname: Berenguer
authors.forename: M A
authors.initials: MA
authors.lastname: de Pedro
authors.forename: J L
authors.initials: JL
authors.lastname: Carrascosa
mesh_terms: D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002458:Cell Fractionation; D003460:Crystallization; D004492:Edetic Acid / Q000494:pharmacology; D005583:Fourier Analysis; D005613:Freeze Etching; D050356:Lipid Metabolism; D008854:Microscopy, Electron; D010457:Peptidoglycan / Q000378:metabolism; D011108:Polymers; D011487:Protein Conformation; D016963:Thermus thermophilus / Q000378:metabolism / Q000648:ultrastructure*; D014764:Viral Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D010457:Peptidoglycan; D011108:Polymers; D014764:Viral Proteins; C074553:p100 protein, Human herpesvirus 6; D004492:Edetic Acid; D002118:Calcium