  Recent experiments by Y. Gambin et al. [PNAS 103, 2098 (2006)] have called
into question the applicability of the Saffman-Delbruck diffusivity for
proteins embedded in the lipid bilayers. We present a simple argument to
account for this observation that should be generically valid for a large class
of transmembrane and membrane bound proteins. Whenever the protein-lipid
interactions locally deform the membrane, that deformation generates new
hydrodynamic stresses on the protein-membrane complex leading to a suppression
of its mobility. We show that this suppression depends on the protein size in a
manner consistent with the work of Y. Gambin et al.
