Abstract
In this paper we investigate the effect of three different types of surfactants, on the hydrolysis of Cytochrome c (Cyt c), a predominantly α helical protein containing a heme group, promoted by [Ce(α PW11O39)2]10- (CeK) and [Zr(α PW11O39)2]10- (ZrK) polyoxometalates. In the presence of SDS, Zw3 12, or CHAPS surfactants, which are commonly used for solubilizing hydrophobic proteins, the specificity of CeK or ZrK toward hydrolysis of Cyt c does not change. However, the hydrolysis rate of Cyt c by CeK was increased in the presence of SDS, but decreased in the presence of CHAPS, and was nearly inhibited in the presence of Zw3 12. The Circular dichroism and Tryptophan fluorescence spectroscopy have shown that the structural changes in Cyt c caused by surfactants are similar to those caused by POMs, hence the same specificity in the absence or presence of surfactants was observed. The results also indicate that for Cyt c hydrolysis to occur, large unfolding of the protein is needed in order to accommodate the POMs. While SDS readily unfolds Cyt c, the protein remains largely folded in the presence of CHAPS and Zw3 12. Addition of POMs to Cyt c solutions in CHAPS results in unfolding of the structure allowing the interaction with POMs to occur and results in protein hydrolysis. Zw3 12, however, locks Cyt c in a conformation that resists unfolding upon addition of POM, and therefore results in nearly complete inhibition of protein hydrolysis.
Highlights
Membrane proteins perform key functions in crucial processes at the interface between the intraand extracellular environment (Tan et al, 2008)
Most of the POMtargeted peptide bonds were at an aspartic acid or glutamic acid residue, and the POM affinity to cleave at these amide bonds remained the same in the presence of 0.5% CHAPS. Encouraged by this result, in this paper we investigate the effect of three different types of surfactants on the hydrolysis of Cytochrome c (Cyt c), a predominantly α-helical protein containing a heme group (Bushnell et al, 1990), promoted by [Ce(α-PW11O39)2]10− (CeK) and [Zr(α-PW11O39)2]10− (ZrK) polyoxometalates
In this work we examine the effect of three different surfactants, which are used in the study of membrane proteins, on the selectivity and the efficiency of the hydrolysis
Summary
Membrane proteins perform key functions in crucial processes at the interface between the intraand extracellular environment (Tan et al, 2008). Atypical or dysfunctional behavior of membrane proteins often presents itself in a range of diseases. Identifying these abnormal membrane proteins might result in novel therapeutic targets (Carter et al, 2004). Membrane proteins are often underrepresented in proteomic studies (Santoni et al, 2000; Whitelegge et al, 2003; Seddon et al, 2004; Speers and Wu, 2007; Tan et al, 2008; Rabilloud, 2009), even though the predicted number of membrane associated proteins is sizable (Wallin and von Heijne, 1998) Their limited representation is attributed to their low abundance
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