Mutational analysis of genes involved in glycogen degradation in Escherichia coli

[摘要] ENGLISH ABSTRACT: Escherichia coli accumulate or degrade glycogen depending on environmental carbon supply. Glycogen synthesis is carried out when carbon is plentiful but other nutrients such as nitrogen is low. Three enzymes, GlgC (ADP-glucose pyrophosphorylase), GlgA (glycogen synthase) and GlgB (glycogen branching enzyme) directs this process to form a branched homopolysaccharide that consists of linear chains of α-1,4-linked glucose monomers, with α-1,6-linked branches. Glycogen degradation is, in turn, carried out by GlgP (glycogen phosphorylase) and GlgX (glycogen debranching enzyme), under starvation conditions.It is known that GlgP and GlgX are the two primary enzymes involved in glycogen breakdown, yet in previous work it was demonstrated that a ΔglgP/ΔglgX double mutant does not eliminate glycogen degradation, indicating that another enzyme must be involved. Given the similarity in structures of glycogen and maltodextrins, MalP was a good candidate to be that enzyme. It shares a similar catalytic activity to that of GlgP, but has a different substrate preference, although there are reports of it acting on glycogen.This study, therefore, aimed to examine the role of MalP, GlgP and GlgX in E. coli by creating a series of knockout mutants lacking combinations of all three enzymes and analysing their ability to degrade glycogen. Additionally, these mutants were studied under scanning electron microscopy to determine whether these mutations had an effect on cell morphology. We demonstrate that in addition to the three genes, there is another gene involve in mobilising glycogen and we observed elongated cell lengths for the strains mutated in malP.

[发布机构] Stellenbosch University