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Photoreaction Dynamics of Full-Length Phototropin from Chlamydomonas reinhardtii
journal contribution
posted on 2019-12-12, 23:03 authored by Yusuke Nakasone, Masumi Ohshima, Koji Okajima, Satoru Tokutomi, Masahide TerazimaPhototropin (phot) is a blue light sensor involved in
the light
responses of several species from green algae to higher plants. Phot
consists of two photoreceptive domains (LOV1 and LOV2) and a Ser/Thr
kinase domain. These domains are connected by a hinge and a linker
domain. So far, studies on the photochemical reaction dynamics of
phot have been limited to short fragments, and the reactions of intact
phot have not been well elucidated. Here, the photoreactions of full-length
phot and of several mutants from Chlamydomonas reinhardtii (Cr) were investigated by the transient grating
and circular dichroism (CD) methods. Full-length Cr phot is in monomeric form in both dark and light states and shows
conformational changes upon photoexcitation. When LOV1 is excited,
the hinge helix unfolds with a time constant of 77 ms. Upon excitation
of LOV2, the linker helix unfolds initially followed by a tertiary
structural change of the kinase domain with a time constant of 91
ms. The quantum yield of conformational change after adduct formation
of LOV2 is much smaller than that of LOV1, indicating that reactive
and nonreactive forms exist. The conformational changes associated
with the excitations of LOV1 and LOV2 occur independently and additively,
even when they are excited simultaneously. Hence, the role of LOV1
is not to enhance the kinase activity in addition to LOV2 function;
we suggest LOV1 has different functions such as regulation of intermolecular
interactions.