Institute for Stem Cell Biology and Regenerative Medicine
In vivo-grown protein crystals have been proposed to occur under positive selection pressure in several organisms. Several biological functions that include insulin secretion sorting of secretory proteins in the Golgi apparatus, pathogenesis of Bacillus thuringiensis, storage mechanisms for infectious viruses and developmental proteins in seeds and eggs are known. While crystallization of proteins inside cells is well known, we recently reported the first atomic resolution (1.2 Å) structure from in vivo grown protein crystals solved by sulfur single-wavelength anomalous dispersion phasing using lower energy X-rays. These are crystals of lipocalin-like milk protein from the pacific beetle cockroach. This protein crystallizes in vivo in the midgut of milk-drinking cockroach embryos. These crystals serve as calorie intense complete nutrients for the embryo development. The normal understanding is that in vitro crystallization requires highly pure and homogeneous proteins. The structures determined by us reveals a motif that is heterogeneous in protein sequence, glycosylation as well as the bound lipid. In vitro expression and secretion of the milk protein in yeast is in progress.
Recently we have also observed similar crystals in the growing stages of the fruit fly. We are now in the processes of isolating these crystals and characterizing them. The talk will present the published results as well as work done after that.
- S. Banerjee, N.P. Coussens NP, F-X. Gallat, N. Sathyanarayanan, J. Srikanth, K.J. Yagi, J.S. Gray, S.S. Tobe, B. Stay, L.M.G. Chavas & S. Ramaswamy, Structure of a heterogeneous, glycosylated, lipid-bound, in vivo-grown protein crystal at atomic resolution from the viviparous cockroach Diploptera punctata. (2016) IUCrJ 3: 282–293.