Characterization and Analysis of Terminal Emitter Subunits in Cyanobacterial PBS Antenna Complex

Physical and Analytical Chemistry Seminar

Lecturer: Maayan Suissa Szlejf

14-14 Jul 2019 @ 12:30

Location: Faculty Seminar Room

Characterization and analysis of terminal emitter subunits in cyanobacterial PBS antenna complex

Maayan Suissa Szlejf, מעיין סויסה שלייף

The major light harvesting antenna in cyanobacteria is the phycobilisome (PBS). The PBS typically contains different subunits, and energy efficiently flows from high (phycocyanin, PC) to low (allophycocyanin, APC) energy absorbing subunits. The smallest PBS identified to date is that of Acaryochloris marina (A. marina), composed of a single rod. The crystal structure of A.marina phycocyanin (PC), the major phycobiliprotein (PBP) component of the A.marina PBS, was determined to be a heterodimer of two alpha and beta isoforms, superimposed in the asymmetric unit of the PC monomer structure (Bar-Zvi et al. 2018). Several AmPC types were isolated, among them a PC type exhibiting allophycocyanin (APC)-like characteristics, suggesting it can efficiently serve as the PBS terminal emitter, since in A.marina a terminal emitter component (usually APC680) was not identified. The lack of APC in the A. marina, along with the novel PC types, suggest that the A.marina PBS may operate without APC, solely based on one multi-functional PC. Here we focus on structure determination of this APC-like PC.
In comparison, a mutant strain of S.elongatus PCC 7942 (olive), which lacks PC rods in its PBS due to an inflicted DNA mutation (Bhalerao et al. 1995; Sendersky et al. 2015), relies only on core cylinders containing APC in order to sustain itself. Since the inner arrangement of the subunits and linkers in the cylinder is apparently important to the organism and is yet unclear, we focused on isolation of the core from the mutant cyanobacteria in order to determine its structure and significance in the photosynthetic process.