Selectivity and Reactivity of ZrIV and CeIV Substituted Keggin Type Polyoxometalates Toward Cytochrome c in Surfactant Solutions

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.

Hydrolysis of Peptide Bonds in Protein Micelles Promoted by a Zirconium(IV)‐Substituted Polyoxometalate as an Artificial Protease

“…However, in the case of ac onsiderably smaller globular protein, Cyt c, which consists of 104 amino acids, it was demonstrated that the addition of surfactants caused largec hanges in the tertiary structure of the protein, which prevented effective interactions with the POM and resulted in ad ecrease in the protein hydrolysis rate. [73]…”

Selective Hydrolysis of Transferrin Promoted by Zr-Substituted Polyoxometalates

“…In the last few years our research group has been developing a new class of artificial metalloproteases based on metal-oxo-based materials and on metal-substituted polyoxometalates, which are able to selectively hydrolyze proteins under mild experimental conditions while producing larger peptide fragments [ 9 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Polyoxometalates are a large class of inorganic metal-oxygen clusters which are composed of transition metals in their highest oxidation state.…”

Effect of [Zr(α-PW11O39)2]10− Polyoxometalate on the Self-Assembly of Surfactant Molecules in Water Studied by Fluorescence and DOSY NMR Spectroscopy

“…The POM, [Zr(α-PW 11 O 39 ) 2 ] 10− (1), is used as the salt, (Et 2 NH 2 ) 10 [Zr(α-PW 11 O 39 ) 2 ] throughout the study. This POM has previously been shown to exhibit catalytic activity towards the hydrolysis of different proteins [13,14].…”

“…In the case of the hydrolysis of hydrophobic proteins, a common approach to circumvent the low solubility (or often insolubility) of the proteins in aqueous solution is to use surfactants. However, as the surfactants exhibit polar or charged headgroups, they can also be involved in a variety of electrostatic or hydrogen bonding interactions with the POM [13]. This could hinder the binding of the POM to a protein, or it could inhibit their catalytic activity [14].…”

“…The POM, [Zr(α-PW11O39)2] 10− (1), is used as the salt, (Et2NH2)10[Zr(α-PW11O39)2] throughout the study. This POM has previously been shown to exhibit catalytic activity towards the hydrolysis of different proteins [13,14]. In this work, we first explore the effect of 1 on the CMC using fluorescence spectroscopy, which is then followed by detailed 1 H and 31 P DOSY studies [21][22][23].…”