β-Glucosidase activator protein from bovine spleen (“coglucosidase”)

“…The main line of evidence for a direct binding of Sap C to glucosylceramidase was the observation that Sepharose-linked Sap C acted as an affinity column for the enzyme [12]. It must be noted that the enzyme loaded on the affinity column was not purified and that the elution buffer contained Triton X-100, a detergent that has a strong affinity for both the activator protein [21] and glucosylceramidase. Thus, binding of glucosylceramidase to the Sepharose-linked Sap C might in fact reflect interactions of the two proteins with some lipid present in the enzyme preparation or/and with Triton X-100.…”

Section: Physical Interaction Between Sap C Ps Luv Andmentioning

confidence: 99%

Function of saposin C in the reconstitution of glucosylceramidase by phosphatidylserine liposomes

et al. 1993

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The function of saposin C (Sap C), a glucosylceramidase activator protein, in the enzyme stimulation by phosphatidylserine (PS) liposomes has been investigated. Using gel filtration experiments evidence was obtained for Sap C binding to PS large unilamellar vesicles (LUV) but not to glucosylceramidase. PS LUV, which by themselves are unable to tightly bind and stimulate the enzyme, acquire the capacity to also bind the enzyme after interaction with Sap C, making it express its full activity. Our results indicate that the primary step in the Sap C mode of action resides in its association with PS membranes; in turn, this association promotes the interaction between the membranes and glucosylceramidase.

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“…The highest level of catalytic activity observed for glucocerebrosidase, in vitro, is dependent on the presence of two small activator proteins, saposin C and saposin A ( Fig. 1; HO et al, 1973;Berent & Radin, 1981) as well as acidic phospholipids (Ho & Light, 1973;Dale et al, 1976). The negative charge of the phospholipid appears to be essential and phospholipids containing short or polyunsaturated fatty acids are the most effective activators .…”

mentioning

confidence: 98%

Identification of the binding and activating sites of the sphingolipid activator protein, saposin C, with glucocerebrosidase

et al. 1995

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Saposin C is a sphingolipid activator protein of 8.5 kDa that activates lysosomal glucocerebrosidase. Previously, we synthesized and characterized a synthetic full-length human saposin C protein that displays 85% of the activity of the native saposin C. In this study we use shorter synthetic peptides derived from the saposin C sequence to map binding and activation sites. By determining the activity and kinetic constant (Kact) values of these peptides, we have identified two functional domains, each comprising a binding site adjacent to or partially overlapping with an activation site. Domains 1 and 2 are located within amino acid positions 6-34 and 41-60, respectively. The activation sites span residues 27-34 and 41-49, whereas binding sites encompass residues 6-27 and 45-60. Peptides containing the sequences of either domain displayed 90% of the activity of the full-length synthetic saposin c. Domain 2, however, bound to glucocerebrosidase by at least an order of magnitude more strongly than domain 1. Binding sites within these domains contain sequences that are excellent candidates for forming amphipathic helical structures. Competition assays demonstrated that the binding of one domain to glucocerebrosidase prevents binding of the other domain, and that saposin A and saposin C bind to the same sites on glucocerebrosidase. A model predicting a saposin C:glucocerebrosidase complex with a stoichiometry of 4:2, respectively, is presented.

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β-Glucosidase activator protein from bovine spleen (“coglucosidase”)

Cited by 59 publications

References 42 publications

Glycolipid and Glycoprotein Degradation

Glycolipid and Glycoprotein Degradation

Function of saposin C in the reconstitution of glucosylceramidase by phosphatidylserine liposomes

Identification of the binding and activating sites of the sphingolipid activator protein, saposin C, with glucocerebrosidase

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