How adding a single methylene to dihydrofolate reductase can change its conformational dynamics

Area of Science:

• Biochemistry
• Molecular Biology
• Microbial Physiology

Background:

• Piezophilic microbes thrive under high pressure, but their proteins' pressure responses are understudied compared to mesophilic counterparts.
• Dihydrofolate reductase (DHFR) is crucial for folate metabolism in all organisms.
• Previous studies on DHFR revealed a single amino acid substitution (aspartic acid to glutamic acid) can invert pressure-dependent activity profiles.

Purpose of the Study:

• To investigate how a single amino acid mutation in dihydrofolate reductase influences protein behavior under varying hydrostatic pressure.
• To elucidate the molecular mechanisms by which this mutation alters pressure-dependent activity using computational simulations.

Main Methods:

• Comparative analysis of homologous dihydrofolate reductase proteins from piezophilic and mesophilic organisms.
• Molecular dynamics simulations were employed to model protein behavior.
• Analysis of residue-level interactions and correlated motions within the protein structure.

Main Results:

• The substitution of aspartic acid with glutamic acid significantly alters the pressure response of DHFR activity.
• Molecular dynamics simulations revealed that the glutamic acid side chain's increased flexibility impacts helix-sheet coupling.
• This change in flexibility propagates, altering correlated motions in distant protein regions, thereby modulating pressure sensitivity.

Conclusions:

• A single amino acid substitution can profoundly alter a protein's response to hydrostatic pressure.
• The observed changes in pressure effects are linked to altered intramolecular communication and flexibility, not direct active site involvement.
• This highlights the subtle yet significant role of specific residues in protein adaptation to extreme environments.