Goddard-Borger Ethan D, Williams Spencer J
ACRF Chemical Biology Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia.
Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia.
Biochem J. 2017 Feb 20;474(5):827-849. doi: 10.1042/BCJ20160508.
The sulfonated carbohydrate sulfoquinovose (SQ) is produced in quantities estimated at some 10 billion tonnes annually and is thus a major participant in the global sulfur biocycle. SQ is produced by most photosynthetic organisms and incorporated into the sulfolipid sulfoquinovosyl diacylglycerol (SQDG), as well as within some archaea for incorporation into glycoprotein N-glycans. SQDG is found mainly within the thylakoid membranes of the chloroplast, where it appears to be important for membrane structure and function and for optimal activity of photosynthetic protein complexes. SQDG metabolism within the sulfur cycle involves complex biosynthetic and catabolic processes. SQDG biosynthesis is largely conserved within plants, algae and bacteria. On the other hand, two major sulfoglycolytic pathways have been discovered for SQDG degradation, the sulfo-Embden-Meyerhof-Parnas (sulfo-EMP) and sulfo-Entner-Doudoroff (sulfo-ED) pathways, which mirror the major steps in the glycolytic EMP and ED pathways. Sulfoglycolysis produces C3-sulfonates, which undergo biomineralization to inorganic sulfur species, completing the sulfur cycle. This review discusses the discovery and structural elucidation of SQDG and archaeal N-glycans, the occurrence, distribution, and speciation of SQDG, and metabolic pathways leading to the biosynthesis of SQDG and its catabolism through sulfoglycolytic and biomineralization pathways to inorganic sulfur.
磺化碳水化合物磺基喹诺糖（SQ）的年产量估计约为100亿吨，因此是全球硫生物循环的主要参与者。大多数光合生物都会产生SQ，并将其整合到硫脂磺基喹诺糖基二酰基甘油（SQDG）中，在一些古细菌中，SQ还会被整合到糖蛋白N-聚糖中。SQDG主要存在于叶绿体的类囊体膜中，它似乎对膜结构和功能以及光合蛋白复合物的最佳活性很重要。硫循环中的SQDG代谢涉及复杂的生物合成和分解代谢过程。植物、藻类和细菌中的SQDG生物合成在很大程度上是保守的。另一方面，已经发现了两条主要的磺基糖酵解途径用于SQDG的降解，即磺基糖酵解途径（sulfo-EMP）和磺基糖酵解途径（sulfo-ED），它们反映了糖酵解EMP和ED途径中的主要步骤。磺基糖酵解产生C3-磺酸盐，这些磺酸盐会生物矿化形成无机硫物种，从而完成硫循环。本文综述了SQDG和古细菌N-聚糖的发现和结构解析、SQDG的存在、分布和形态，以及导致SQDG生物合成及其通过磺基糖酵解和生物矿化途径分解为无机硫的代谢途径。
