Question

How can a protein act as a signal integrating sensor?

Answer 1

Proteins that sense signals and transmit them are called sensor proteins. They are the sensor proteins as in bacteria those involved in the chemotactic signal transduction and in higher organisms in the secondary messenger system.

In bacterial chemotaxis, the chemoreceptors are the signal integrating sensor proteins. They are also transmembrane integral dimer proteins. They exist as dimers with a signal recognition site facing the outside environment where in the chemical signal binds to the protein. These proteins are called methyl-accepting chemotaxis proteins (MCPs). These are methyl receptors as the carboxyl groups gets methylated in response to an encounter with chemotactic signals. The number of methylation provides a quantitative estimation of the level of the signal received and these methylated carboxyl groups are temporary responses and storage of information of the chemotactic signals.

In higher organisms, the calcium sensing proteins are such signal integrating sensor proteins. example of such proteins are calmodulin, calnexin, calreticulin, gelsolin.