Ludovic Pélosi

Twelve populations of Escherichia coli evolved in and adapted to a glucose-limited environment from a common ancestor. We used two-dimensional protein electrophoresis to compare two evolved clones, isolated from independently derived populations after 20,000 generations. Exceptional parallelism was detected. We compared the observed changes in protein expression profiles with previously characterized global transcription profiles of the same clones; this is the first time such a comparison has been made in an evolutionary context where these changes are often quite subtle. The two methodologies exhibited some remarkable similarities that highlighted two different levels of parallel regulatory changes that were beneficial during the evolution experiment. First, at the higher level, both methods revealed extensive parallel changes in the same global regulatory network, reflecting the involvement of beneficial mutations in genes that control the ppGpp regulon. Second, both methods detected expression changes of identical gene sets that reflected parallel changes at a lower level of gene regulation. The protein profiles led to the discovery of beneficial mutations affecting the malT gene, with strong genetic parallelism across independently evolved populations. Functional and evolutionary analyses of these mutations revealed parallel phenotypic decreases in the maltose regulon expression and a high level of polymorphism at this locus in the evolved populations.

Barley (1,3)-beta-D-glucan endohydrolases (EC ), inactivated by site-directed mutagenesis of their catalytic nucleophiles, show autocondensation glucosynthetic activity with alpha-laminaribiosyl fluoride and heterocondensation glycosynthetic activity with alpha-laminaribiosyl fluoride and 4'-nitrophenyl beta-D-glucopyranoside. The native enzyme is a retaining endohydrolase of the family 17 group and catalyzes glycosyl transfer reactions at high substrate concentrations. Catalytic efficiencies (k(cat) K(m)(-1)) of mutants E231G, E231S, and E231A as glycosynthases are 28.9, 0.9, and 0.5 x 10(-4) m(-1) s(-1), respectively. Glycosynthase reactions appear to be processive and proceed with pH optima of 6-8 and yields of up to 75%. Insoluble products formed during the glycosynthase reaction appear as lamellar, hexagonal crystals when observed by electron microscopy. Methylation, NMR, and matrix-assisted laser desorption ionization time-of-flight analyses show that the reaction products are linear (1,3)-beta-D-glucans with a degree of polymerization of 30-34, whereas electron and x-ray diffraction patterns indicate that these (1,3)-beta-D-glucan chains adopt a parallel, triple helical conformation. The (1,3)-beta-D-glucan triple helices are orientated perpendicularly to the plane of the lamellar crystals. The barley (1,3)-beta-D-glucan glycosynthases have considerable potential for tailored and high efficiency synthesis of (1,3)-beta-D-linked oligo- and polysaccharides, some of which could have immunomodulating activity, or for the coupling of (1,3)-beta-D-linked glucosyl residues onto other oligosaccharides or glycoproteins.

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