Molecular basis of thermal stability in truncated (2/2) hemoglobins.
BACKGROUND
Understanding the molecular mechanism through which proteins are functional at extreme high and low temperatures is one of the key issues in structural biology. To investigate this phenomenon, we have focused on two instructive truncated hemoglobins from Thermobifida fusca (Tf-trHbO) and Mycobacterium tuberculosis (Mt-trHbO); although the two proteins are structurally nearly identical, only the former is stable at high temperatures.


METHODS
We used molecular dynamics simulations at different temperatures as well as thermal melting profile measurements of both wild type proteins and two mutants designed to interchange the amino acid residue, either Pro or Gly, at E3 position.


RESULTS
The results show that the presence of a Pro at the E3 position is able to increase (by 8°) or decrease (by 4°) the melting temperature of Mt-trHbO and Tf-trHbO, respectively. We observed that the ProE3 alters the structure of the CD loop, making it more flexible.


CONCLUSIONS
This gain in flexibility allows the protein to concentrate its fluctuations in this single loop and avoid unfolding. The alternate conformations of the CD loop also favor the formation of more salt-bridge interactions, together augmenting the protein's thermostability.


CONCLUSIONS
These results indicate a clear structural and dynamical role of a key residue for thermal stability in truncated hemoglobins.
Departamento de Química Inorgánica, Analítica y Química Física, INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
Juan P
JP
Bustamante
Instituto Pasteur, Fondazione Cenci Bolognetti, Department of Biochemical Sciences, University of Rome "La Sapienza", Italy.
Alessandra
A
Bonamore
Departamento de Química Biológica, IQUIBICEN-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
Alejandro D
AD
Nadra
Instituto Pasteur, Fondazione Cenci Bolognetti, Department of Biochemical Sciences, University of Rome "La Sapienza", Italy.
Natascia
N
Sciamanna
Instituto Pasteur, Fondazione Cenci Bolognetti, Department of Biochemical Sciences, University of Rome "La Sapienza", Italy.
Alberto
A
Boffi
Departamento de Química Inorgánica, Analítica y Química Física, INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina. Electronic address: dario@qi.fcen.uba.ar.
Darío A
DA
Estrin
Instituto de Cálculo, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina. Electronic address: lboechi@ic.fcen.uba.ar.
Leonardo
L
Boechi
D000192:Actinomycetales / Q000737:chemistry / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009169:Mycobacterium tuberculosis / Q000737:chemistry / Q000378:metabolism*; D055550:Protein Stability; D054793:Truncated Hemoglobins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism
D054793:Truncated Hemoglobins
Folding; Molecular dynamics; Mycobacterium tuberculosis; Thermobifida fusca; Thermostability; Truncated hemoglobin