Chlorophyll a with a farnesyl tail in thermophilic cyanobacteria

Abstract

Photosystem II (PSII) of oxygenic photosynthetic organisms normally contains exclusively chlorophyll a (Chl a) as its major light-harvesting pigment. Chl a canonically consists of the chlorin headgroup with a 20 carbon, 4 isoprene unit, phytyl tail. We have examined the 1.9 Å crystal structure of PSII from thermophilic cyanobacteria reported by Shen and coworkers in 2012 (PDB accession of 3ARC/3WU2). A newly refined electron density map from this structure, presented here, reveals that some assignments of the cofactors may be different from those modeled in the 3ARC/3WU2 structure, including a specific Chl a that appears to have a truncated tail by one isoprene unit. We provide experimental evidence using high performance liquid chromatography and mass spectrometry for a small population of Chl a esterified to a 15 carbon farnesyl tail in PSII of thermophilic cyanobacteria.

Identification of a Na+-Binding Site near the Oxygen-Evolving Complex of Spinach Photosystem II

“…PSII-enriched thylakoid membrane fragments were prepared from spinach as previously described and suspended in a buffer containing 15 mM NaCl, 20 mM MES, and 30% (v/v) ethylene glycol. − The pH was adjusted to 6.0 with NaOH. Suspended and purified PSII membranes were stored in liquid nitrogen.…”

The terminal enzymes of (bacterio)chlorophyll biosynthesis

“…Open Sci. 9: 211903 subunit of the PSII complex [103]. Esterification of Chlide with FPP is presumably catalysed by ChlG; indeed, ChlG has been shown to use exogenous FPP as a substrate [11].…”

“…A small population of Chls are esterified with a shorter farnesyl moiety (Chl a f ) in some species of thermophilic cyanobacteria. These Chl a f molecules appear to specifically localize within the CP43 subunit of the PSII complex [103]. Esterification of Chlide with FPP is presumably catalysed by ChlG; indeed, ChlG has been shown to use exogenous FPP as a substrate [11].…”

Structural basis of light‐harvesting in the photosystem II core complex

“…Electrostatic computations predict this special hydrogen bond to cause a blue‐shift of the corresponding Chl absorption, but it remains to be clarified, whether the electrostatic model is sufficient to describe such an interaction. Another special property of Chl C4 is that is has been suggested to possess a farnesyl tail (15 carbon atoms) at the 17 3 ‐ester instead of the common phytyl chain (20 carbon atoms) based on a refinement of the 3ARC/3WU2 structure at a resolution of 1.9 Å (refined to 5V2C, see Table ) . In the RT structure 6DHE, the Chl C4 chain is modeled with 14 carbon atoms and rather as a truncated phytyl than a farnesyl tail (Figure b).…”