Mutational analysis of genes involved in glycogen degradation in Escherichia coli

Strydom, Lindi (2016-12)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

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.

AFRIKAANS OPSOMMING: Escherichia coli vergader of breek glikogeen af na gelang van koolstof beskikbaarheid in die omgewing. Glikogeen sintese word uitgevoer wanneer koolstof volop is en ander voedingstowwe soos stikstof laag is. Drie ensieme, GlgC (ADP-glukose pirofosforilase), GlgA (glikogeen sintase) en GlgB (glikogeen vertakkingsensiem) regeer hierdie proses om 'n vertakte homopolisakkaried te vorm wat bestaan uit lineêre kettings van α-1,4-gekoppelde glukose monomere met α-1,6-gekoppelde takke. Glikogeen afbraak word, op sy beurt, deur GlgP (glikogeen fosforilase) en GlgX (glikogeen onvertakkings ensiem) uitgevoer, onder hongersnood kondisies. Dit is bekend dat GlgP en GlgX die twee primêre ensieme is wat by glikogeen afbraak betrokke is, maar in vorige werk is daar getoon dat glikogeen afbraak nie geelimineer word in 'n ΔglgP/ΔglgX dubbel mutant nie, wat dui daarop dat nog 'n ensiem betrokke moet wees. Aangesien die struktuur van glikogeen en maltodekstrine baie dieselfde is, was MalP 'n goeie kandidaat. Dit deel 'n soortgelyke katalitiese aktiwiteit aan diè van GlgP, maar dit het 'n voorkeur vir 'n ander substraat, alhoewel daar verslae is wat rapporteer dat dit ook kan inwerk op glikogeen. Hierdie studie is dus daarop gemik om die rol van MalP, GlgP en GlgX in E. coli te ondersoek deur ‘n reeks delesie mutante te skep wat ontbreek in kombinasies van al drie ensieme en sodoende hul vermoë om glikogeen af te breek, te ontleed. Verder is hierdie mutante bestudeer onder skandeerelektronmikroskopie om vas te stel of hierdie mutasies 'n uitwerking op selmorfologie het. Ons demonstreer dat benewens tot die drie gene, is daar nog 'n geen betrokke in die mobilisering van glikogeen, en verlengde sel lengtes is waargeneem vir die stamme gemuteerd in malP.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100148
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