Abstract
The signal recognition particle (SRP) is a ubiquitous system for the targeting of membrane and secreted proteins. The chloroplast SRP (cpSRP) is unique among SRPs in that it possesses no RNA and is functional in post-translational as well as co-translational targeting. cpSRP is present within two pools in the chloroplast: a co-translationally active SRP54 homologue (cpSRP54) and a post translationally active cpSRP, which is a complex of cpSRP54 and the novel SRP component, cpSRP43. The presence or absence of cpSRP43 seems to determine the targeting activity of cpSRP54. cpSRP43 has the following modules: Chromo1, Ank1-4, Chromo2 and Chromo3. The recent studies show that the Chromo2 is required for both targeting complex formation and integration because this module interacts with cpSRP54. Hence, Chromo2 plays a crucial role in the formation of “transit complex” contains cpSRP54, cpSRP43 and Lhcb1 which is responsible for targeting the proteins into the chloroplast and into the thylakoid membrane. In this context, we tempted to solve the solution structure of Chromo2 domain using multi-dimensional NMR spectroscopy. We carried out variety of three dimensional NMR experiments such as, 15N-HSQC NOESY, 15N-HSQC TOCSY, HNCA, HN(CO)CA and HNHA. Also, we preformed 2D NOESY& TOCSY. Assignments of all protons, 15N and 13Ca have been done using 2D NOESY& TOCSY, HSQC 15N-HSQC NOESY, 15N-HSQC TOCSY, HNCA and HNCA datasets. TALOS and CSI are performed to predict dihedral angles and secondary structure of Chromo2. The structure is being calculated by dynamical simulated annealing protocol using ARIA (which is a structure calculation software generous provided by Michael Nigles). Also, we characterized Chromo2 domain using biophysical techniques such as UV-CD, Fluorescence, and FPLC. The results will be discussed in greater detail.