title: A calcium-gated lid and a large beta-roll sandwich are revealed by the crystal structure of extracellular lipase from Serratia marcescens.
abstract: Lipase LipA from Serratia marcescens is a 613-amino acid enzyme belonging to family I.3 of lipolytic enzymes that has an important biotechnological application in the production of a chiral precursor for the coronary vasodilator diltiazem. Like other family I.3 lipases, LipA is secreted by Gram-negative bacteria via a type I secretion system and possesses 13 copies of a calcium binding tandem repeat motif, GGXGXDXUX (U, hydrophobic amino acids), in the C-terminal part of the polypeptide chain. The 1.8-A crystal structure of LipA reveals a close relation to eukaryotic lipases, whereas family I.1 and I.2 enzymes appear to be more distantly related. Interestingly, the structure shows for the N-terminal lipase domain a variation on the canonical alpha/beta hydrolase fold in an open conformation, where the putative lid helix is anchored by a Ca(2+) ion essential for activity. Another novel feature observed in this lipase structure is the presence of a helical hairpin additional to the putative lid helix that exposes a hydrophobic surface to the aqueous medium and might function as an additional lid. The tandem repeats form two separated parallel beta-roll domains that pack tightly against each other. Variations of the consensus sequence of the tandem repeats within the second beta-roll result in an asymmetric Ca(2+) binding on only one side of the roll. The analysis of the properties of the beta-roll domains suggests an intramolecular chaperone function.
authors.affiliation: Department of Chemistry and Biochemistry, University Bern Freiestrasse 3, CH-3012 Bern, Switzerland.
authors.forename: Reto
authors.initials: R
authors.lastname: Meier
authors.forename: Thomas
authors.initials: T
authors.lastname: Drepper
authors.forename: Vera
authors.initials: V
authors.lastname: Svensson
authors.forename: Karl-Erich
authors.initials: KE
authors.lastname: Jaeger
authors.forename: Ulrich
authors.initials: U
authors.lastname: Baumann
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D016384:Consensus Sequence; D018360:Crystallography, X-Ray; D057927:Hydrophobic and Hydrophilic Interactions; D008049:Lipase / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017354:Point Mutation; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012706:Serratia marcescens / Q000201:enzymology*; D013059:Spectrum Analysis, Raman; D020080:Tandem Repeat Sequences
chemical_list: D001426:Bacterial Proteins; D008049:Lipase; D002118:Calcium