RESUMO
Sperm-specific glyceraldehyde-3-phosphate dehydrogenase (GAPDS) is bound to the fibrous sheath of the sperm flagellum through the hydrophobic N-terminal domain of the enzyme molecule. Expression of human GAPDS in E.coli cells yields inactive and insoluble protein. Presumably, the N-terminal domain prevents correct folding of the full-length recombinant enzyme. To obtain GAPDS in a soluble and active form, a recombinant enzyme lacking in 68 amino acids of the N-terminal domain (dN-GAPDS) was expressed in E.coli cells. Purified dN-GAPDS was shown to be a protein of 9.3 nm in diameter (by dynamic light scattering), which is close to the size of the muscle tetrameric glyceraldehyde-3-phosphate dehydrogenase (8.6 nm). The catalytic properties of the protein differed a little from those of the muscle glyceraldehyde-3-phoshate dehydrogenase. However, compared to muscle glyceraldehyde-3-phoshate dehydrogenase, dN-GAPDS exhibited enhanced thermostability (the transition midpoints values are 60.8 and 67.4°C, respectively) and was much more resistant towards action of guanidine hydrochloride (inactivation constants are 2.45±0.018 and 0.118 ± 0.008 min(-1), respectively). The enhanced stability of dN-GAPDS is likely to be related to some specific features of the GAPDS structure compared to that of the muscle enzyme: 1) reduced number of solvent-exposed salt bridges; 2) 2 additional buried salt bridges; and 3) 6 additional proline residues in GAPDS meeting the "proline rule". It is assumed that high stability of the sperm-specific GAPDS is of importance for the efficiency of fertilization.
Assuntos
Gliceraldeído-3-Fosfato Desidrogenases/metabolismo , Proteínas Recombinantes/metabolismo , Espermatozoides/enzimologia , Sequência de Aminoácidos , Substituição de Aminoácidos , Animais , Sítios de Ligação/genética , Biocatálise , Estabilidade Enzimática , Escherichia coli/genética , Gliceraldeído-3-Fosfato Desidrogenases/química , Gliceraldeído-3-Fosfato Desidrogenases/genética , Temperatura Alta , Humanos , Concentração de Íons de Hidrogênio , Cinética , Masculino , Modelos Moleculares , Dados de Sequência Molecular , Músculos/enzimologia , Mutação , Prolina/química , Prolina/genética , Prolina/metabolismo , Desnaturação Proteica , Estrutura Terciária de Proteína , Coelhos , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Homologia de Sequência de AminoácidosRESUMO
Influence of polyelectrolytes of different chemical structure and degree of polymerization on aggregation and denaturation of the oligomeric enzyme glyceraldehyde-3-phosphate dehydrogenase has been studied to ascertain molecular characteristics of the polymer chains providing the efficient prevention of aggregation of the enzyme without drastic changes in its structure and catalytic activity. The best polymers meeting these requirements were found to be hydrophilic high-molecular-weight polyelectrolytes forming stable complexes with the enzyme. The revealed pronounced negative effect of short polymer chains on the enzyme must be taken into account in the design of protein-polyelectrolyte systems by using thoroughly fractionated polymer samples containing no admixture of charged oligomers.
