Sandbox Reserved 774

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Protein surfaces near the active site are characterized by a positive electrostatic potential. In each structure there are several multi-chain carbonyl groups without hydrogen bonding partners in the active site. These could act in a proton transfer pathway by helping locate water molecules. Around the acetyl group, there exists a hydrophobic pocket which would stabilize the neutral charge while the substrate is bound to the enzyme once the amino group is deprotonated.
Protein surfaces near the active site are characterized by a positive electrostatic potential. In each structure there are several multi-chain carbonyl groups without hydrogen bonding partners in the active site. These could act in a proton transfer pathway by helping locate water molecules. Around the acetyl group, there exists a hydrophobic pocket which would stabilize the neutral charge while the substrate is bound to the enzyme once the amino group is deprotonated.
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==Kinetic Mechanism==
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The binding of substrates and release of products can be random, fully ordered, or a combination of both. It operates on a Bi-Bi mechanism.
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==Chemical Mechanism==
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After the formation of a ternary complex of acetyl-CoA, histone and enzyme, an active site base deprotonates lysin, which allows for direct attack of the N-e-lysine on the carbonyl carbon of acetyl-CoA.
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The analysis of a loss-of-function mutant of the hpa2 gene suggests that the hpa2 affects bacterial proliferation in host plants and a hypersensitive response in nonhost plants. As this is the first of such enzyme activity identified in the Hrp protein family, we speculate that the Hpa2 contributes to the assembly of the TTSS by enlarging gaps in the peptidoglycan meshwork of bacterial cell walls
The analysis of a loss-of-function mutant of the hpa2 gene suggests that the hpa2 affects bacterial proliferation in host plants and a hypersensitive response in nonhost plants. As this is the first of such enzyme activity identified in the Hrp protein family, we speculate that the Hpa2 contributes to the assembly of the TTSS by enlarging gaps in the peptidoglycan meshwork of bacterial cell walls
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'''SHIVA'''
 

Revision as of 01:51, 27 November 2013

This Sandbox is Reserved from Sep 25, 2013, through Mar 31, 2014 for use in the course "BCH455/555 Proteins and Molecular Mechanisms" taught by Michael B. Goshe at the North Carolina State University. This reservation includes Sandbox Reserved 299, Sandbox Reserved 300 and Sandbox Reserved 760 through Sandbox Reserved 779.
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Contents

Introduction

My protein is Histone Acetyltransferase Hpa2. Hpa2 is a member of the GNAT (Gcn5-related N-acetyltransferases) super-family of enzymes that are found spread out across nature and use acyl-CoA's to acylate their cognate substrates. Histone Acetyltransferase Hpa2 is found in the organism Saccharomyces Cerevisiae, which is more commonly known as Baker's Yeast. In vitro, Hpa2 serves to acetylate histone H3 'Lys-4' and 'Lys-14' and histone H4 'Lys-5' and 'Lys-12.' In solution, Hpa2 forms a dimer, and upon binding with AcCoA forms a tetramer. It is classified as a transferase.

Structure

Has a chain structure with 2.4 A resolution, and 2.9 A resolution with a co-factor (acetyl-CoA). The method used to determine the structure was X-ray crystallography. Crystal structure analysis clearly shows that Hpa2 is dimeric in solution and tetramerizes in the unit crystal. The average B-factor value is 23.9 (main chain) with a 25.4 side chain. The R-factor is 0.19.

Secondary Structure

Most of the secondary structure elements of the monomer contribute residues in dimer contacts. They form a barrel-like with ten strands in which the component strands of the barrel are locked together.

Description

This structure contains ... alpha helices...

3D Structure

Insert caption here

Drag the structure with the mouse to rotate

Mechanism

Protein surfaces near the active site are characterized by a positive electrostatic potential. In each structure there are several multi-chain carbonyl groups without hydrogen bonding partners in the active site. These could act in a proton transfer pathway by helping locate water molecules. Around the acetyl group, there exists a hydrophobic pocket which would stabilize the neutral charge while the substrate is bound to the enzyme once the amino group is deprotonated.

Kinetic Mechanism

The binding of substrates and release of products can be random, fully ordered, or a combination of both. It operates on a Bi-Bi mechanism.

Chemical Mechanism

After the formation of a ternary complex of acetyl-CoA, histone and enzyme, an active site base deprotonates lysin, which allows for direct attack of the N-e-lysine on the carbonyl carbon of acetyl-CoA.


Implications

The analysis of a loss-of-function mutant of the hpa2 gene suggests that the hpa2 affects bacterial proliferation in host plants and a hypersensitive response in nonhost plants. As this is the first of such enzyme activity identified in the Hrp protein family, we speculate that the Hpa2 contributes to the assembly of the TTSS by enlarging gaps in the peptidoglycan meshwork of bacterial cell walls

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