Investigation on the metal binding sites of a putative Zn(ii) transporter in opportunistic yeast species Candida albicans

Abstract

The protein fragment C4YJH2 of Candida albicans has the ability to tightly coordinate Zn(ii) at its C-terminal region by means of an evolutionarily well-conserved histidine-rich sequence.

Novel insights into the metal binding ability of ZinT periplasmic protein from Escherichia coli and Salmonella enterica

“…This trend has been observed in many other systems and ascribed to the possible electronic effect of serine residues, capable of favouring the amidic proton displacement by the Cu(II) ion. 44,45,51 The metal binding behaviour of the ZinT fragments is fully consistent with the previously formulated hypotheses about the protein biological role. The high efficacy of HGHHXH in metal chelation is in line with the necessity to recover and stabilize as much micronutrients as possible from the medium, acting as a primary metal scavenger.…”

“…The histidine-rich fragments L1 and L2 are better ligands for the Zn( ii ) ion, confirming the general assumption that a higher number of histidine residues favour the metal complexation. 45–47 Indeed, according to the proposed speciation models, the ZinT short fragments form stable 4N complexes with Zn( ii ) already at pH around 6. In contrast, L3 and L4 contain only 3 imidazole groups and they can only coordinate the metal ion by means of a (3N Im , O − ) binding mode.…”

“…This trend has been observed in many other systems and ascribed to the possible electronic effect of serine residues, capable of favouring the amidic proton displacement by the Cu( ii ) ion. 44,45,51…”

Zn2+ and Cu2+ Binding to the Extramembrane Loop of Zrt2, a Zinc Transporter of Candida albicans

“…In the case of L1 and L1_S6A, we could observe, from the competition plot reported in Figure 4 a, that the presence of serine stabilized copper complexes above pH 6.5, i.e., when the metal ion began to interact with backbone amides. Although this behavior is not fully elucidated, it quite frequently occurs in Cu 2+ complexes with peptides, and it is also experimentally verified by several other systems studied in the same or similar conditions [ 10 , 24 , 25 ]. Therefore, we suggest a possible electronic effect of serines adjacent to the donor residues, that makes the amidic proton displacement more favorable.…”

“…We t hus decided to study the thermodynamic and coordination properties of Zn 2+ and Cu 2+ complexes with the model peptides corresponding to the identified metal binding sequences: Ac-GPHTHSHFGD-NH 2 (L1), Ac-PSHFAHAQEHQDP-NH 2 (L2) and Ac-DDEEEDLE-NH 2 (L3); we introduced the terminal protection to simulate the behavior of the native fragment within the protein. According to previous studies, the presence of a serine residue in the peptide sequence may favor the displacement of amidic protons by the copper ion, affecting the complex formation ability of the investigated systems [ 10 ]. Therefore, in order to verify this property, we also studied the Ser-to-Ala mutants of the wild-type peptides: Ac-GPHTHAHFGD-NH 2 (L1_S6A) and Ac-PAHFAHAQEHQDP-NH 2 (L2_S2A).…”