Cooperativity of catalytic and lectin-like domain ofT. congolensetrans-sialidase modulates its catalytic activity

Abstract

Trans-sialidases (TS) represent a multi-gene family of unusual enzymes, which catalyse the transfer of terminal sialic acids from sialoglycoconjugates to terminal galactose or N-acetylgalactosamine residues of oligosaccharides without the requirement of CMP-Neu5Ac, the activated Sia used by typical sialyltransferases. Most work on trypanosomal TS has been done on enzymatic activities of TS from T. cruzi (causing Chagas disease in Latin America), subspecies of T. brucei, (causing human sleeping sickness in Africa) and T. congolense (causing African Animal Trypanosomosis in livestock). Previously, we demonstrated that T. congolense TS (TconTS) lectin domain (LD) binds to several carbohydrates, such as 1,4-β-mannotriose. To investigate the influence of TconTS-LD on enzyme activities, we firstly performed in silico analysis on structure models of TconTS enzymes. Findings strongly supports the potential of domain swaps between TconTS without structural disruptions of the enzymes overall topologies. Recombinant domain swapped TconTS1a/TS3 showed clear sialidase and sialic acid (Sia) transfer activities, when using fetuin and lactose as Sia donor and acceptor substrates, respectively. While Sia transfer activity remained unchanged from the level of TconTS1a, hydrolysis was drastically reduced. Presence of 1,4-β-mannotriose during TS reactions modulates enzyme activities favouring trans-sialylation over hydrolysis. In summary, this study provides strong evidence that TconTS-LDs play pivotal roles in modulating enzyme activity and biological functions of these and possibly other TS, revising our fundamental understanding of TS modulation and diversity.

N-glycosylation modulates enzymatic activity ofTrypanosoma congolensetrans-sialidase

“…Similar results were found in single-site N -glycosylation mutants of the IBV spike protein by circular dichroism experiments (5). The observed thermal stability of TconTS1 might be explained by the high β-sheet content of the protein as well as by an extended interface between CD and LD stabilized by salt bridges and a well-structured hydrogen bond network, making unfolding rather unlikely (35). Although N -glycans do not seem to influence the stability of TconTS1 after successful expression, glycans are known to be required for proper protein folding (3).…”

“…Like all TS, TconTS1 consists of an N -terminal catalytic domain (CD) responsible for the transfer of Sia, and of a C-terminal lectin-like domain (LD) whose biological function remains unclear. Recently, we demonstrated that TconTS-LD can modulate enzymatic activity (35). CD and LD are connected via an α-helix (Fig.…”