The Influence of the Loop between Residues 223-235 in Beetle Luciferase Bioluminescence Spectra: A Solvent Gate for the Active Site of pH-Sensitive Luciferases

Authors

  • Vadim R. Viviani,

    Corresponding author
    1. Laboratório de Biotecnologia e Bioluminescência, Universidade de Sorocaba (UNISO), Universidade Federal de São Carlos, Campus de Sorocaba, Sorocaba, São Paulo, Brazil
    2. Departamento de Biologia Celular e Molecular, Instituto de Biociências, Universidade Estadual de São Paulo (UNESP), Rio Claro, São Paulo, Brazil
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  • Antonio J. Silva Neto,

    1. Departamento de Biologia Celular e Molecular, Instituto de Biociências, Universidade Estadual de São Paulo (UNESP), Rio Claro, São Paulo, Brazil
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  • Frederico G. C. Arnoldi,

    1. Departamento de Biologia Celular e Molecular, Instituto de Biociências, Universidade Estadual de São Paulo (UNESP), Rio Claro, São Paulo, Brazil
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  • João A. R. G. Barbosa,

    1. Centro de Biologia Molecular Estrutural, Laboratório Nacional de Luz Síncrotron, Campinas, São Paulo, Brazil
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  • Yoshihiro Ohmiya

    1. Cell Dynamics Research Group, National Institute of Advanced Science and Technology (AIST), Osaka, Japan
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*email: viviani@power.ufscar.br (Vadim Viviani)

Abstract

Beetle luciferases emit a wide range of bioluminescence colors, ranging from green to red. Firefly luciferases can shift the spectrum to red in response to pH and temperature changes, whereas click beetle and railroadworm luciferases do not. Despite many studies on firefly luciferases, the origin of pH-sensitivity is far from being understood. Through comparative site-directed mutagenesis and modeling studies, using the pH-sensitive luciferases (Macrolampis and Cratomorphus distinctus fireflies) and the pH-insensitive luciferases (Pyrearinus termitilluminans, Phrixotrix viviani and Phrixotrix hirtus) cloned by our group, here we show that substitutions dramatically affecting bioluminescence colors in both groups of luciferases are clustered in the loop between residues 223-235 (Photinus pyralis sequence). The substitutions at positions 227, 228 and 229 (P. pyralis sequence) cause dramatic redshift and temporal shift in both groups of luciferases, indicating their involvement in labile interactions. Modeling studies showed that the residues Y227 and N229 are buried in the protein core, fixing the loop to other structural elements participating at the bottom of the luciferin binding site. Changes in pH and temperature (in firefly luciferases), as well as point mutations in this loop, may disrupt the interactions of these structural elements exposing the active site and modulating bioluminescence colors.

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