title: Structural basis for metal ion coordination and the catalytic mechanism of sphingomyelinases D.
abstract: Sphingomyelinases D (SMases D) from Loxosceles spider venom are the principal toxins responsible for the manifestation of dermonecrosis, intravascular hemolysis, and acute renal failure, which can result in death. These enzymes catalyze the hydrolysis of sphingomyelin, resulting in the formation of ceramide 1-phosphate and choline or the hydrolysis of lysophosphatidyl choline, generating the lipid mediator lysophosphatidic acid. This report represents the first crystal structure of a member of the sphingomyelinase D family from Loxosceles laeta (SMase I), which has been determined at 1.75-angstrom resolution using the "quick cryo-soaking" technique and phases obtained from a single iodine derivative and data collected from a conventional rotating anode x-ray source. SMase I folds as an (alpha/beta)8 barrel, the interfacial and catalytic sites encompass hydrophobic loops and a negatively charged surface. Substrate binding and/or the transition state are stabilized by a Mg2+ ion, which is coordinated by Glu32, Asp34, Asp91, and solvent molecules. In the proposed acid base catalytic mechanism, His12 and His47 play key roles and are supported by a network of hydrogen bonds between Asp34, Asp52, Trp230, Asp233, and Asn252.
authors.affiliation: Department of Physics, Instituto de Biociências, Letras e Ciências Exatas/Universidade Estadual Paulista, São José do Rio Preto, SP 15054-000, Brazil.
authors.forename: Mário T
authors.initials: MT
authors.lastname: Murakami
authors.forename: Matheus F
authors.initials: MF
authors.lastname: Fernandes-Pedrosa
authors.forename: Denise V
authors.initials: DV
authors.lastname: Tambourgi
authors.forename: Raghuvir K
authors.initials: RK
authors.lastname: Arni
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D019281:Dimerization; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010727:Phosphoric Diester Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D013111:Spider Venoms / Q000201:enzymology; D013112:Spiders
chemical_list: D007477:Ions; D008670:Metals; D013111:Spider Venoms; C055161:loxosceles venom; D010727:Phosphoric Diester Hydrolases; C055160:sphingomyelin phosphodiesterase D