Is thermosensor DesK a bifunctional protein having kinase and channel activities?

CYBULSKI LARISA ESTEFANÍA

Valparaíso

Congreso; VIII congreso Iberoamericano de Biofísica- XI Reunión Annual Sociedad Chilena de Neurociencias-; 2013

Sociedad Chilena de Neurociencias

DesK is involved in detecting temperature changes in Bacillus subtillis. At low temperatures it behaves as a kinase, phosphorylating the response regulator DesR, which in turn activates expression of a desaturase, thereby regulating membrane fluidity. We designed a chimerical protein in which both sensing and transmission of DesK(which has five transmembrane segments), were captured into one single chimerical transmembrane segment (MS-DesK). Employing genetics, biophysical and molecular biology tools, we found that both the N-terminus and the C-terminus of DesK and MS-DesK have motifs that render DesK sensitive to membrane thickness and interfacial hydration, which would in turn depend upon temperature changes. Both motifs must interact to form the trigger. Our proposed mechanism of thermal regulation holds true for both, the full length DesK and the Minimal sensor DesK. Then the emerging questions are : What is the role of the other transmembrane segments? Why were they conserved along evolution if they could have been replaced by only one TMS? Our hypothesis that DesK is a bifunctional protein with two separatable activities: i) a thermosensitive histidine kinase that responds to low temperatures activating desaturase expression and ii) an ion chanel. The idea that DesK could be also anion channel is reinforced by : i) the presence of several Ser and Thr residues in the TM region, ii) DesK has an cluster of charged resiudes at the interfacial region connecting the TMS with the catalytic domain conserved in several ion channels and iii) DesK activity is strongly influenced by salt concentrations.