# The Photosynthetic Complexes of Thylakoid Membranes of Photoautotrophs and a Quartet of Their Polar Lipids

## TL;DR

This paper explores the role of polar lipids in photosynthetic complexes and their specific interactions with proteins and amino acids in thylakoid membranes.

## Contribution

The paper investigates the exact localization and roles of polar lipids within photosynthetic complexes and their interactions with proteins.

## Key findings

- Polar lipids are found inside photosystem II, photosystem I, and cytochrome b6f complexes.
- Lipids are located at the borders between monomers of super complexes like PSII-LHCII and PSI-LHCI.
- The paper discusses the distinct roles of polar lipid head groups and fatty acid chains in photosynthesis.

## Abstract

The important function of polar lipids in the biochemical chains of photosynthesis, the outstanding biochemical process on our planet, has been mentioned in many publications. Over the last several years, apart from the known function of lipids in creating a matrix for photosynthetic complexes, most attention has been paid to the role of lipids in building up and functioning of the photosynthetic complexes. The lipid molecules are found inside the complexes of photosystem II (PSII), photosystem I (PSI), and cytochrome b6f (Cyt b6f) together with other cofactors that accompany proteins and chlorophyll molecules. Super complexes PSII-light-harvesting complex II (PSII-LHCII) and PSI-light-harvesting complex I (PSI-LHCI) also include lipid molecules; part of the lipid molecules is located at the borders between the separate monomers of the complexes. Our interest is in the exact localization of lipid molecules inside the monomers: what are the protein subunits with the lipid molecules in between and how do the lipids contact directly with the amino acids of the proteins? The photosystems include very few classes of all the polar lipids, three groups of glyceroglycolipids, and one group of glycerophospholipids make up the quartet of polar lipids. What are the reasons they have been selected for the role? There are no doubts that the polar heads and the fatty acids chains of these lipids are taking part in the processes of photosynthesis. However, what are the distinct roles for each of them? The advantages and disadvantages of the head groups of lipids from thylakoid membranes and those lipids that for various reasons could not take their place are discussed. Attention is focused on those bound fatty acids that predominate or are characteristic for each class of thylakoid lipids. Emphasis is also placed on the content of each of the four lipids in all photosynthetic complexes, as well as on contacts of head groups and acyl chains of lipids with specific proteins, transmembrane chains, and their amino acids. This article is devoted to the search for answers to the questions posed.