Functional assignment for the N-terminal segments of cyanobacterial Hli proteins

Václav VINCIK

Bachelor's thesis

Abstract:

Light harvesting antennas (LHC) of green algae and plants are unique in their ability to alternate between light harvesting, where absorbed energy is transferred to photosystems, and photoprotection, where this energy is dissipated as heat. This thesis examines their cyanobacterial ancestors, the High light-inducible proteins (Hlips). The model cyanobacterium, Synechocystis PCC 6803, contains a set of four Hlips (HliA-D) that bind two different pigments (chlorophyll and -carotene), form a specific set of homo- and heterodimers, and, finally, recognize other protein partners (Ycf39, Chl-synthase, CP47). However, the mechanism of how Hlips recognize their protein partners is unclear. This thesis aims to clarify the importance of the Hlip-specific N-terminus and the highly conserved transmembrane helix in preventing homo-dimerization of HliA and HliB and binding PSII-assembly-related protein. According to a recent hypothesis, the N-terminus is solely responsible for recognizing PSII factors and subunits, while the membrane helix determines the specificity of Hlip-Hlip interactions. To address this model, Synechocystis strains producing chimeric Hlips were synthesized, each fusing the N-terminal domain from one Hlip with the transmembrane helix from another, followed by their purification and characterization of the interaction with other proteins and pigments.

Abstract:

Light harvesting antennas (LHC) of green algae and plants are unique in their ability to alternate between light harvesting, where absorbed energy is transferred to photosystems, and photoprotection, where this energy is dissipated as heat. This thesis examines their cyanobacterial ancestors, the High light-inducible proteins (Hlips). The model cyanobacterium, Synechocystis PCC 6803, contains a set of four Hlips (HliA-D) that bind two different pigments (chlorophyll and -carotene), form a specific set of homo- and heterodimers, and, finally, recognize other protein partners (Ycf39, Chl-synthase, CP47). However, the mechanism of how Hlips recognize their protein partners is unclear. This thesis aims to clarify the importance of the Hlip-specific N-terminus and the highly conserved transmembrane helix in preventing homo-dimerization of HliA and HliB and binding PSII-assembly-related protein. According to a recent hypothesis, the N-terminus is solely responsible for recognizing PSII factors and subunits, while the membrane helix determines the specificity of Hlip-Hlip interactions. To address this model, Synechocystis strains producing chimeric Hlips were synthesized, each fusing the N-terminal domain from one Hlip with the transmembrane helix from another, followed by their purification and characterization of the interaction with other proteins and pigments.

Language used: English

Date on which the thesis was submitted / produced: 8. 12. 2023

Thesis defence

• Supervisor: doc. Ing. Roman Sobotka, Ph.D.

UNIVERSITY OF SOUTH BOHEMIA IN ČESKÉ BUDĚJOVICE

Faculty of Science

Bachelor programme / field:
Biology / Biology