posted on 2023-07-26, 15:11authored byNikolai P. Skiba, Tylor R. Lewis, William J. Spencer, Carson M. Castillo, Andrej Shevchenko, Vadim Y. Arshavsky
Photoreceptor cells generate neuronal signals in response
to capturing
light. This process, called phototransduction, takes place in a highly
specialized outer segment organelle. There are significant discrepancies
in the reported amounts of many proteins supporting this process,
particularly those of low abundance, which limits our understanding
of their molecular organization and function. In this study, we used
quantitative mass spectrometry to simultaneously determine the abundances
of 20 key structural and functional proteins residing in mouse rod
outer segments. We computed the absolute number of molecules of each
protein residing within an individual outer segment and the molar
ratio among all 20 proteins. The molar ratios of proteins comprising
three well-characterized constitutive complexes in outer segments
differed from the established subunit stoichiometries of these complexes
by less than 7%, highlighting the exceptional precision of our quantification.
Overall, this study resolves multiple existing discrepancies regarding
the outer segment abundances of these proteins, thereby advancing
our understanding of how the phototransduction pathway functions as
a single, well-coordinated molecular ensemble.