Structural Propensity in the C‐terminal Domain of the Albino3 Translocase in Thylakoids

Abstract

The c terminus of the Albino3 (Alb3) translocase in chloroplasts is a region fundamental to the integration of LHCPs into the thylakoid membrane in cooperation with the cpSRP. Alb3 is an integral membrane protein containing five transmembrane helices in an N‐in, C‐out orientation in the thylakoid membrane. The c terminus of Alb3 is responsible for recruiting the cpSRP43 subunit of cpSRP to the thylakoid membrane for successful integration of LHCPs. This region of Alb3 has previously been described as intrinsically disordered. In more recent developments, intrinsically disordered proteins have been shown to carry out vital functions within cells. While our findings show that cAlb is predominately disordered, we have discovered a region in this protein which has a high propensity towards an ordered structure. This region was first isolated by secondary structural sequence analysis using multiple prediction software. Single point mutations which would contribute to the displacement of structure were made within this region, followed by structural characteristic analysis. Results derived from Far‐UV‐Circular Dichroism, intrinsic fluorescence, and trypsin digestion reveal that the mutations show a decrease in overall structure. Inter‐residue distance and energetics were acquired from smFRET analysis of this region, in its native state and upon denaturation. Differences in smFRET histograms show the region is able to be unfolded with increasing denaturant. Additionally, computational methods show a structural propensity in this region and agree with the smFRET results. These combined biophysical and computational results reveal a region of structure in the N‐terminal of cAlb. The local structure found in this study may prove to be important to the binding event with the cpSRP43 subunit of cpSRP Support or Funding Information Department of Energy (DOE)