title: Understanding enzymatic mechanism and allostery using macromolecular rate theory

authors: Grout, Emily Katherine

subjects: Biochemistry

abstract: Intricate systems of regulation at many levels act to control enzyme rates to tune metabolism across biosynthetic pathways. Allostery is a ubiquitous regulatory mechanism for feedback and regulation of enzymes in biosynthetic pathways. ATP-phosphoribosyltransferase from Mycobacterium tuberculosis (mtuATP-PRT) catalyses the first committed step in de novo histidine biosynthesis, and allosteric product inhibition of ATP-PRT by L-His is key to regulating metabolic flux in this pathway. mtuATP-PRT also exhibits allosteric activation by a histidine analogue 3 (2-Thienyl)-L-alanine (TIH). This compound binds in the same allosteric site as L-His and appears to elicit a structurally identical “tensed” conformation, apparently contradicting previous suggestions that the tensed conformation drives inhibitory regulation in mtuATP-PRT. 

Through mutations adjacent to the allosteric binding site, we have interrupted allosteric inhibition by L-His while retaining allosteric activation by TIH. Kinetic assays of wild type ATP-PRT and mutants across a large temperature range with various allosteric effects, has identified dynamic changes between allosterically modulated states of the enzyme, and suggests an enthalpy-entropy (∆H‡-∆S‡) trade off occurring in allosteric states. 

Complementing our kinetic data, crystallographic analysis and molecular dynamics (MD) simulations of wild type and mutant ATP-PRT have identified two residues that differ upon the binding of TIH (in comparison to L-His binding). Glu-18 and Arg-27 rotate between ligand bound states and form interacting bonds in L-His bound structures that may serve to stabilise and reduce the overall flexibility of the hexameric conformation. This Glu-18 and Arg-27 interaction varies between L-His-bound, APO-mtuATP-PRT and TIH-bound structures, suggesting this interaction may demarcate allosteric activation and inhibition.

An evolutionary analysis of ATP-PRT was undertaken and has identified the long form of ATP-PRT as the ancestral form, and the short form ATP-PRT has subsequently co-opted a histidyl-tRNA synthetase (HisRS) gene product (HisZ) as its regulatory domain. Aminoacyl-tRNA synthetases are known to be prone to horizontal gene transfer, therefore the co-option of HisRS and the loss of the C-terminal domain in ATP-PRTs provides an evolutionary trajectory for diverse ATP-PRT isoforms.

text: Understanding enzymatic mechanism and allostery using macromolecular rate theory Intricate systems of regulation at many levels act to control enzyme rates to tune metabolism across biosynthetic pathways. Allostery is a ubiquitous regulatory mechanism for feedback and regulation of enzymes in biosynthetic pathways. ATP-phosphoribosyltransferase from Mycobacterium tuberculosis (mtuATP-PRT) catalyses the first committed step in de novo histidine biosynthesis, and allosteric product inhibition of ATP-PRT by L-His is key to regulating metabolic flux in this pathway. mtuATP-PRT also exhibits allosteric activation by a histidine analogue 3 (2-Thienyl)-L-alanine (TIH). This compound binds in the same allosteric site as L-His and appears to elicit a structurally identical “tensed” conformation, apparently contradicting previous suggestions that the tensed conformation drives inhibitory regulation in mtuATP-PRT. 

Through mutations adjacent to the allosteric binding site, we have interrupted allosteric inhibition by L-His while retaining allosteric activation by TIH. Kinetic assays of wild type ATP-PRT and mutants across a large temperature range with various allosteric effects, has identified dynamic changes between allosterically modulated states of the enzyme, and suggests an enthalpy-entropy (∆H‡-∆S‡) trade off occurring in allosteric states. 

Complementing our kinetic data, crystallographic analysis and molecular dynamics (MD) simulations of wild type and mutant ATP-PRT have identified two residues that differ upon the binding of TIH (in comparison to L-His binding). Glu-18 and Arg-27 rotate between ligand bound states and form interacting bonds in L-His bound structures that may serve to stabilise and reduce the overall flexibility of the hexameric conformation. This Glu-18 and Arg-27 interaction varies between L-His-bound, APO-mtuATP-PRT and TIH-bound structures, suggesting this interaction may demarcate allosteric activation and inhibition.

An evolutionary analysis of ATP-PRT was undertaken and has identified the long form of ATP-PRT as the ancestral form, and the short form ATP-PRT has subsequently co-opted a histidyl-tRNA synthetase (HisRS) gene product (HisZ) as its regulatory domain. Aminoacyl-tRNA synthetases are known to be prone to horizontal gene transfer, therefore the co-option of HisRS and the loss of the C-terminal domain in ATP-PRTs provides an evolutionary trajectory for diverse ATP-PRT isoforms.

year: 2022

title: Cost- and income-based measures of human capital

authors: Le, Trinh

subjects: human capital

abstract: Human capital is increasingly believed to play an important role in the growth process, however, adequately measuring its stock remains controversial. In this paper three general approaches to measurement are identified; cost‐based, income‐based and educational stock‐based. This survey focuses on the first two approaches and provides a critical review of the theories and their applications to data from a range of countries. Particular emphasis is placed upon the work of Jorgenson and Fraumeni (1989, 1992) and some new results for New Zealand based upon their approach are also presented.

text: Cost- and income-based measures of human capital Human capital is increasingly believed to play an important role in the growth process, however, adequately measuring its stock remains controversial. In this paper three general approaches to measurement are identified; cost‐based, income‐based and educational stock‐based. This survey focuses on the first two approaches and provides a critical review of the theories and their applications to data from a range of countries. Particular emphasis is placed upon the work of Jorgenson and Fraumeni (1989, 1992) and some new results for New Zealand based upon their approach are also presented.

year: 2003

title: Reducing our prison population: Past failures and new approaches

authors: Tauri, Juan Marcellus

abstract: Earlier this year the Minister of Justice, Andrew Little announced the latest in a long line of reviews, taxpayer-funded summits and inter-agency, ‘wholeof-government’ projects stretching back to the late-1980s, all aimed in some form or other, at making the criminal justice system more ‘safe’ and ‘effective’. Officially launched at a summit held in Porirua in August 2018, the aim of the latest review is to reduce New Zealand’s prison muster by 30% over the next 15 years. And unsurprisingly, given our significant over-representation in prisons, a specific focus of the review is on identifying ways to significantly reduce Māori over-representation in the prison population. This commentary represents a modest offering in response to the current government’s stated aim of making the justice system safer and more effective, and to reduce the prison muster, and it is based on two core arguments, namely that successive governments and the public service have failed to reduce offending and imprisonment and that successful solutions require community empowerment and government/public service accountability.

text: Reducing our prison population: Past failures and new approaches Earlier this year the Minister of Justice, Andrew Little announced the latest in a long line of reviews, taxpayer-funded summits and inter-agency, ‘wholeof-government’ projects stretching back to the late-1980s, all aimed in some form or other, at making the criminal justice system more ‘safe’ and ‘effective’. Officially launched at a summit held in Porirua in August 2018, the aim of the latest review is to reduce New Zealand’s prison muster by 30% over the next 15 years. And unsurprisingly, given our significant over-representation in prisons, a specific focus of the review is on identifying ways to significantly reduce Māori over-representation in the prison population. This commentary represents a modest offering in response to the current government’s stated aim of making the justice system safer and more effective, and to reduce the prison muster, and it is based on two core arguments, namely that successive governments and the public service have failed to reduce offending and imprisonment and that successful solutions require community empowerment and government/public service accountability.

year: 2019