Manganese binding to the 23 kDa extrinsic protein of Photosystem II

Abstract

The recombinant form of the extrinsic 23 kDa protein (psbP) of Photosystem II (PSII) was studied with respect to its capability to bind Mn. The stoichiometry was determined to be one manganese bound per protein. A very high binding constant, K(A)=10(-17) M(-1), was determined by dialysis of the Mn containing protein against increasing EDTA concentration. High Field EPR spectroscopy was used to distinguish between specific symmetrically ligated Mn(II) from those non-specifically Mn(II) attached to the protein surface. Upon Mn binding PsbP exhibited fluorescence emission with maxima at 415 and 435 nm when tryptophan residues were excited. The yield of this blue fluorescence was variable from sample to sample. It was likely that different conformational states of the protein were responsible for this variability. The importance of Mn binding to PsbP in the context of photoactivation of PSII is discussed.

Initial Steps of Photosystem II de Novo Assembly and Preloading with Manganese Take Place in Biogenesis Centers in Synechocystis

“…As it is known that Mn 2+ prefers such ligands, it seems likely that these residues are involved in loose attachment of Mn 2+ to the surface of PratA. A similar effect has been described for PsbP, for which a stoichiometry of 10 Mn 2+ :1 PsbP has been found; however, further analyses revealed two different binding modes as well, as most Mn 2+ ions were also merely bound with a low affinity to the Asp/Glu-containing surface of PsbP (Bondarava et al, 2007). The exact localization of the high-affinity Mn 2+ binding site for PratA including the amino acids involved has to be determined in future work.…”

“…The observed K d1 value is in the range of affinities of other Mn 2+ binding proteins, such as the Mn-dependent catalase MnCat (K d = 40 mM) or the oxidative stress protecting protein SsDPS (K d = 48 mM) (Meier et al, 1996;Crowley et al, 2000;Pierce et al, 2003;Hayden and Hendrich, 2010). Nevertheless, much higher binding constants for Mn 2+ to protein have been reported, for instance, in case of MnSOD and PsbP proteins (Mizuno et al, 2004;Bondarava et al, 2007). It has to be taken into account, however, that metal binding to these proteins is irreversible, in contrast with PratA, for which we postulate a function in Mn 2+ transport and, thus, transient Mn 2+ binding.…”

“…Only one periplasmic Mn binding protein (MncA) has been described to date (Tottey et al, 2008), but its precise function remains to be elucidated. In vascular plants, the extrinsic PSII proteins PsbP and PsbO have been reported to bind Mn (Abramowicz and Dismukes, 1984;Bondarava et al, 2007), but these proteins help to stabilize the Mn cluster and do not transport Mn to the WOC (Roose et al, 2007).…”

The Conserved His-144 in the PsbP Protein Is Important for the Interaction between the PsbP N-terminus and the Cyt b559 Subunit of Photosystem II

“…In the spinach PsbP model a Zn 2ϩ ion is ligated through the His-144 and Asp-165 residues, while the tobacco PsbP crystallizes in the absence of Zn 2ϩ ions (22,33). The Glu-177 residue was speculated to be a metalbinding residue (26); however, its distance from the Zn 2ϩ ion is relatively far (ϳ11 Å) in spinach PsbP. In tobacco PsbP, His-144 is likely to form a salt bridge (ϳ3.6 Å) with the carboxyl group of Asp-165.…”

“…This Zn 2ϩ -binding domain is conserved in the structure of CyanoP. PsbP has been reported to bind Mn 2ϩ ion, and the metal-binding site has been suggested to be around the His-144, 26). The structural conservation may indicate the importance of metal binding for the function of PsbP and CyanoP.…”