Studies of the catabolism of two unusual types of sialoglycoconjugates, KDN-containing glycoconjugates and G(M2) ganglioside
Description
Complex carbohydrates are catabolized by glycohydrolases, which exhibit anomeric, glycon, aglycon and linkage specificities. The structures of complex carbohydrates are known to play an important role in their catabolism. For example, a small change in the chemical substituents (e.g., 4-O-acetylation or changing 5-acetamido to 5-OH) of the pyranose ring of sialic acid can cause this sugar to become resistant to regular (N-acetylneuraminic acid-cleaving) sialidases. Another example is the unusual interaction of the two terminal sugars, N-acetylgalactosamine and sialic acid, in ganglioside G$\sb{\rm M2}$, which causes a requirement for a specific protein cofactor to permit its degradation by $\beta$-hexosaminidase A. The study of the catabolism of such unusual glycoconjugates provides important new insights into how the structure of the sugar chain can regulate its biodegradation. This dissertation consists of two parts: (1) The study of the catabolism of KDN-(deaminated neuraminic acid, 3-deoxy- scD-glycero- scD-galacto-2-nonulosonic acid, 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid) containing glycoconjugates. This part includes a description of the first identification and characterization of KDN-sialidase from loach liver, a new type of glycoconjugate-cleaving enzyme that can catabolize KDN-glycoconjugates. This part of the dissertation also includes a description of two distinct sialidases, KDN-sialidase and regular sialidase, in starfish; (2) the study of G$\sb{\rm M2}$ catabolism in vitro by an acidic $\beta$-hexosaminidase from mouse liver and comparison with G$\sb{\rm M2}$ catabolism by human liver $\beta$-hexosaminidase A. In part 2, evidence is presented that mouse Hex A, but not mouse Hex B, can hydrolyze G$\sb{\rm M2}$, with the requirement of G$\sb{\rm M2}$ activator protein. We also present evidence that mouse recombinant G$\sb{\rm M2}$ activator can stimulate the hydrolysis of G$\sb{\rm A2}$ by mouse and human Hex A, and to a lesser extent by mouse Hex B. This data is important for interpreting the results of the Hex A knockout mouse. The ability of mouse and human G$\sb{\rm M2}$ activator protein to cross-stimulate G$\sb{\rm M2}$ hydrolysis by human and mouse Hex A and B is also examined