Suppression of lysozyme aggregation at alkaline pH by tri-N-acetylchitotriose.

Satish Kumar, Vijay Kumar Ravi, Rajaram Swaminathan

Index: Biochim. Biophys. Acta 1794(6) , 913-20, (2009)

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Abstract

Inhibiting protein misfolding and aggregation is imperative for treatment of amyloid diseases. In this regard small molecules which bind to and stabilize the monomeric protein have invited attention owing to their ability to significantly slow down or inhibit aggregation and amyloid formation. We have earlier shown that hen egg-white lysozyme (HEWL) spontaneously forms soluble oligomers at pH 12.2, which are later stabilized by intermolecular disulphide bonds, eventually resulting in amyloid fibrils. In this work, we show that overnight ( approximately 12 h) pre-incubation of HEWL with its competitive inhibitor, N,N',N''-Triacetylchitotriose (chitotriose) at neutral pH, impairs its aggregation and fibrillogenesis at pH 12.2. Unlike in control or N-Acetyl-D-glucosamine (NAG) pre-incubated samples, HEWL-chitotriose complex displayed i) reduced thioflavin T and ANS fluorescence, ii) small oligomers but no amyloid fibrils in AFM, iii) absence of large aggregates in SDS-PAGE and gel-filtration elutions, iv) marginally more helical content in CD spectra and v) >70% enzymatic activity after 24 h and approximately 16% activity after week long incubation at alkaline pH. It is likely that strong binding in the HEWL-chitotriose complex, in contrast to weakly bound HEWL-NAG complex, raises the activation energy barrier for protein misfolding and subsequent aggregation, thereby retarding the aggregation kinetics substantially. These results hold promise for the therapy of human lysozyme amyloidosis.