The Photosystem II Assembly Factor Ycf48 from the Cyanobacterium Synechocystis sp. PCC 6803 Is Lipidated Using an Atypical Lipobox Sequence

Abstract

Photochemical energy conversion during oxygenic photosynthesis is performed by membrane-embedded chlorophyll-binding protein complexes. The biogenesis and maintenance of these complexes requires auxiliary protein factors that optimize the assembly process and protect nascent complexes from photodamage. In cyanobacteria, several lipoproteins contribute to the biogenesis and function of the photosystem II (PSII) complex. They include CyanoP, CyanoQ, and Psb27, which are all attached to the lumenal side of PSII complexes. Here, we show that the lumenal Ycf48 assembly factor found in the cyanobacterium Synechocystis sp. PCC 6803 is also a lipoprotein. Detailed mass spectrometric analysis of the isolated protein supported by site-directed mutagenesis experiments indicates lipidation of the N-terminal C29 residue of Ycf48 and removal of three amino acids from the C-terminus. The lipobox sequence in Ycf48 contains a cysteine residue at the −3 position compared to Leu/Val/Ile residues found in the canonical lipobox sequence. The atypical Ycf48 lipobox sequence is present in most cyanobacteria but is absent in eukaryotes. A possible role for lipoproteins in the coordinated assembly of cyanobacterial PSII is discussed.

The Ycf48 accessory factor occupies the site of the oxygen-evolving manganese cluster during photosystem II biogenesis

“…3b). 34 We found that Ycf48 bound to the lumenal regions of the D1 subunit via an Arg patch consisting of six residues (Ycf48-Arg180, Arg196, Arg215, Arg219, Arg220 and Arg237) (Fig. 3a, b, c).…”

Mass spectrometry analysis of the photosystem II assembly factor Psb27 revealed variations in its lipid modification

“…In general, the observed variance of the Psb27 lipid modification is typical for cyanobacterial lipoproteins since these proteins tend to bind lipids with different fatty acids (Fagerlund and Eaton-Rye 2011; Knoppová et al 2021;Nowaczyk et al 2006;Ujihara et al 2008), which originate from membrane phospholipids (Chattopadhyay and Wu 1977;Lai and Wu 1980). Therefore, the type of lipid modification is determined by the fatty acid composition of the membrane, which in turn changes depending on environmental conditions (Allakhverdiev et al 2001;Gombos et al 1997;Mironov et al 2012).…”

“…Cyanobacterial lipoproteins have been reported both in thylakoid and cytoplasmic membranes (Liberton et al 2016), but in contrast to the Sec-pathway itself (Liberton et al 2016;Nakai et al 1993;Srivastava et al 2005), a maturation pathway for lipidation was not yet identified in cyanobacterial thylakoid membranes (Agarwal et al 2010;Liberton et al 2016), apart from low abundant apolipoprotein N-acyltransferase. If the maturation system is not present in the thylakoid membrane, Psb27 and other photosynthesis related lipoproteins must be transferred efficiently after lipidation to the thylakoid membrane, as they are absent or only in low abundance in the plasma membrane (Ishikawa et al 2005;Knoppová et al 2021;Selão et al 2016). Alternatively, lipoproteins might be specifically modified in the PratA-defined membrane (PDM) region at the interface between plasma and thylakoid membrane (Rast et al 2016) and the transfer could be mediated by maturation centers, where both membranes (Rast et al 2019;Stengel et al 2012).…”

“…Alternatively, lipoproteins might be specifically modified in the PratA-defined membrane (PDM) region at the interface between plasma and thylakoid membrane (Rast et al 2016) and the transfer could be mediated by maturation centers, where both membranes (Rast et al 2019;Stengel et al 2012). Interestingly, lipidation of Ycf48, another auxiliary protein involved in early PSII assembly, occurs during or after its association with the D1 precursor protein (Knoppová et al 2021;Zak et al 2001), most likely within the PDM (Komenda et al 2008;Rast et al 2016), which would further support a localization of the lipidation machinery in the PDM.…”

Specific Incorporation of Polyunsaturated Fatty Acids into the sn-2 Position of Phosphatidylglycerol Accelerates Photodamage to Photosystem II under Strong Light

“…These observations suggest that unusual PG containing PUFAs at the sn -2 position becomes a substrate for lipidation of these lipoproteins, which might affect the stability of the OEC. A recent study by Knoppová et al revealed that a PSII assembly factor, Ycf48, was lipidated by PG [ 41 ]. Therefore, the unstable PSII complex in the presence of PUFAs shown in Figure 3 might be due to the lipidation of Ycf48 by the unusual PG molecules.…”