RESUMEN
The complement system is a key component of innate and adaptive immune responses. Complement regulation is critical for prevention and control of disease. We have determined the crystal structure of the complement regulatory enzyme human factor I (fI). FI is in a proteolytically inactive form, demonstrating that it circulates in a zymogen-like state despite being fully processed to the mature sequence. Mapping of functional data from mutants of fI onto the structure suggests that this inactive form is maintained by the noncatalytic heavy-chain allosterically modulating activity of the light chain. Once the ternary complex of fI, a cofactor and a substrate is formed, the allosteric inhibition is released, and fI is oriented for cleavage. In addition to explaining how circulating fI is limited to cleaving only C3b/C4b, our model explains the molecular basis of disease-associated polymorphisms in fI and its cofactors.
Asunto(s)
Factor I de Complemento/química , Factor I de Complemento/genética , Polimorfismo Genético , Estructura Terciaria de Proteína , Regulación Alostérica , Sitios de Unión/genética , Dominio Catalítico , Complemento C3b/química , Complemento C3b/metabolismo , Complemento C4b/química , Complemento C4b/metabolismo , Factor I de Complemento/metabolismo , Cristalización , Cristalografía por Rayos X , Precursores Enzimáticos/química , Precursores Enzimáticos/genética , Precursores Enzimáticos/metabolismo , Predisposición Genética a la Enfermedad/genética , Glicosilación , Humanos , Modelos Moleculares , Mutación , Unión ProteicaRESUMEN
Complement receptor 1-related protein Y (CrrY) is an important cell-surface regulator of complement that is unique to rodent species. The structure of rat CrrY domains 1-4 has been determined in two distinct crystal forms and reveals a 70° bend between domains 3 and 4. Comparisons of this structure with those of other complement regulators suggests that rearrangement of this interface may occur on forming the regulatory complex with C3b.
Asunto(s)
Antígenos de Superficie/química , Receptores de Superficie Celular/química , Animales , Cristalografía por Rayos X , Humanos , Modelos Moleculares , Estructura Terciaria de Proteína , Ratas , Homología Estructural de ProteínaRESUMEN
CD59 is a membrane-bound glycoprotein that protects host cells from lysis by inhibiting the terminal pathway of complement, preventing the formation and insertion of the membrane attack complex (MAC). Crystals of bacterially expressed and nonglycosylated recombinant soluble human CD59 have been obtained from three crystallization conditions, each of which gave rise to a distinct crystal form. Each crystal form led to a crystal structure at high resolution (1.15, 1.35 and 1.8 A). In one of these structures the electron-density map shows an as yet unidentified small molecule in the predicted C8/C9-binding site. The presence/absence of this ligand is linked to alternate conformations of the amino acids implicated in C8/C9 binding.
Asunto(s)
Antígenos CD59/biosíntesis , Antígenos CD59/química , Escherichia coli/genética , Regulación Bacteriana de la Expresión Génica , Antígenos CD59/genética , Antígenos CD59/metabolismo , Complemento C8/metabolismo , Complemento C9/metabolismo , Cristalografía por Rayos X , Humanos , Proteínas Recombinantes/biosíntesis , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , SolubilidadRESUMEN
SoxB is an essential component of the bacterial Sox sulfur oxidation pathway. SoxB contains a di-manganese(II) site and is proposed to catalyze the release of sulfate from a protein-bound cysteine S-thiosulfonate. A direct assay for SoxB activity is described. The structure of recombinant Thermus thermophilus SoxB was determined by x-ray crystallography to a resolution of 1.5 A. Structures were also determined for SoxB in complex with the substrate analogue thiosulfate and in complex with the product sulfate. A mechanistic model for SoxB is proposed based on these structures.