16 research outputs found

    Conserved main-chain peptide distortions: A proposed role for Ile203 in catalysis by dihydrodipicolinate synthase

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    In recent years, dihydrodipicolinate synthase (DHDPS, E.C. 4.2.1.52) has received considerable attention from a mechanistic and structural viewpoint. DHDPS catalyzes the reaction of (S)-aspartate-β-semialdehyde with pyruvate, which is bound via a Schiff base to a conserved active-site lysine (Lys161 in the enzyme from Escherichia coli). To probe the mechanism of DHDPS, we have studied the inhibition of E. coli DHDPS by the substrate analog, β-hydroxypyruvate. The K i was determined to be 0.21 (±0.02) mM, similar to that of the allosteric inhibitor, (S)-lysine, and β-hydroxypyruvate was observed to cause time-dependent inhibition. The inhibitory reaction with β-hydroxypyruvate could be qualitatively followed by mass spectrometry, which showed initial noncovalent adduct formation, followed by the slow formation of the covalent adduct. It is unclear whether β-hydroxypyruvate plays a role in regulating the biosynthesis of meso-diaminopimelate and (S)-lysine in E. coli, although we note that it is present in vivo. The crystal structure of DHDPS complexed with β-hydroxypyruvate was solved. The active site clearly showed the presence of the inhibitor covalently bound to the Lys161. Interestingly, the hydroxyl group of β-hydroxypyruvate was hydrogen-bonded to the main-chain carbonyl of Ile203. This provides insight into the possible catalytic role played by this peptide unit, which has a highly strained torsion angle (ω ∼201°). A survey of the known DHDPS structures from other organisms shows this distortion to be a highly conserved feature of the DHDPS active site, and we propose that this peptide unit plays a critical role in catalysis

    The effects of pre-enrolment emotions and peer group interaction on students’ satisfaction

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    Higher education institutions are increasingly involved in measuring students' satisfaction and communicating messages to prospective, current, and previous students. A review of the literature suggests that institutions have traditionally focused on cognitive rather than affective measures, and have communicated messages in a media environment that could be dominated by the institution. This paper seeks to contribute by investigating the role of peer-to-peer social network media in evoking emotions about attending university prior to enrolment and subsequent satisfaction with it. A two-stage study involving 519 prospective students from a UK higher education institution were asked about their cognition and emotions one month prior to enrolment and again one month after. Hypotheses related their involvement in online peer-to-peer media to their perceived level of satisfaction, emotions evoked, and likelihood of recommending the institution. It was found that emotions were a better predictor of likelihood of recommendation than cognitive measures of satisfaction. Positive emotions evoked during the pre-enrolment phase led to positive emotions post-enrolment. There was an association between prospective students' level of involvement with online communities prior to enrolment and their level of evoked positive emotions
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