The characterization of hyperthermostable proteins has broadened our understand-ing and presented new opportunities for solvunderstand-ing one of the most challenging problems in biophys
Trang 1M I N I R E V I E W S E R I E S
Protein hyperthermostability – current status and beyond Sotirios Koutsopoulos
Center for Biomedical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
The discovery of hyperthermophilic microorganisms,
thriv-ing at environmental temperatures near or above 100C,
has revolutionized our ideas about the upper limit of
temperature at which life can exist The characterization of
hyperthermostable proteins has broadened our
understand-ing and presented new opportunities for solvunderstand-ing one of the
most challenging problems in biophysics: how is structural
stability and biological function retained at high
tempera-tures where ‘normal’ proteins undergo dramatic structural
changes? The general consensus has been that protein
hyper-thermostability does not involve any aberrant features but
rather is accomplished through modifying only the
distribu-tion of structural features (i.e extended ion pair networks,
increased packing density, decreased number of surface
loops, prevalence of specific amino acids in the sequence,
etc.) that stabilize proteins which are adjusted to other
environmental conditions
This series contains four articles encompassing different
approaches to, and aspects of, protein hyperthermostability
In the first article, Matsui and Harata analyze
crystallo-graphic data from homologous mesophilic, thermophilic and
hyperthermophilic proteins and discuss the importance of
buried polar interactions It has been long suggested that ion
pair interactions are essential to stabilize the protein
struc-ture at high temperastruc-tures Herein, it is proposed that ion
pairs in the core are more important than those on the
surface of hyperthermostable proteins In the second review,
Luke and colleagues carefully distinguish between
hyper-thermophilic and hyper-thermophilic proteins and compare them
with their mesophilic counterparts Thermodynamic and
kinetic data of protein unfolding in vitro reveal remarkable
differences: the study concludes that hyperthermostability is
primarily linked to very slow protein unfolding kinetics This
implies that hyperthermophiles survived by selection of
protein mutants that unfold slowly The third review by
Tehei and Zaccai addresses the role of dynamics on protein
stability Protein atoms are not fixed, as depicted in crystal
structures, but fluctuate Hence, the whole protein fluctuates
as well The dynamic nature of hyperthermostable proteins may be the key to unraveling the mechanism responsible for the delicate balance between rigidity, which is related to heat resistance, and molecular fluctuations at high temperatures, which account for biological function In the last article, Unsworth and colleagues review current theories and suggest that a combination of structural, dynamic and other physi-cochemical attributes are optimized to ensure stability and activity at high temperatures The potential for utilizing heat stable proteins was demonstrated in the PCR reaction, a revolutionary technique in molecular biology This review also summarizes methodologies and proposes strategies for improving heat stability and activity of hyperthermostable proteins for applications in biocatalysis and biotechnology The reviews presented here highlight the significant advances made to date towards understanding protein sta-bility and function at high temperatures, but also raise questions New discoveries have pushed the limits of hyper-thermostability to higher temperatures; is it now necessary
to consider as hyperthermostable only those proteins that are stable at temperatures near 100C and above? In aque-ous media above 100C, hydrophobic interactions and hydrogen bonds are significantly weakened; is this the rea-son why such interactions are not frequently observed as stabilizing factors in hyperthermostable proteins? To date, data have been collected from in vitro studies of dilute pro-tein solutions; are the conclusions valid for intracellular proteins where biomolecular crowding is an important sta-bilizing factor? Structural information for hyperthermosta-ble proteins is derived from diffraction of crystals grown at (or below) room temperature; do these crystal structures represent the structure of these proteins in their native high temperature environment? Advances in protein science will continue to generate more systematic structural and physi-cochemical information on hyperthermostable proteins and the features that underlie their unique properties
Sotirios Koutsopoulos is a Senior Research Fellow in the Center for Biomedical Engineering at the Massachu-setts Institute of Technology (MIT) He received his undergraduate degree in chemistry from the University of Patras, Greece and completed his PhD in the same institute in physical chemistry of biological phenomena He conducted postdoctoral work in the Danish Technical University in nanotechnology and then, as a Marie Curie fellow, in Wageningen University, the Netherlands, studied biophysics, specifically analyzing factors involved in the thermal stability and biological function of hyperthermostable proteins Dr Koutsopoulos joined MIT in 2005
to study protein stability and misfolding in cells.
doi: 10.1111/j.1742-4658.2007.05957.x
FEBS Journal 274 (2007) 4011 ª 2007 The Author Journal compilation ª 2007 FEBS 4011