Membrane proteins comprise ~35% of proteome and imparts essential functionality to the cellular membrane. Compared to soluble proteins, the biogenesis of membrane proteins poses enormous challenges to cells, as these hydrophobic proteins are highly prone to aggregation and misfolding in aqueous cellular environments before arrival at their membrane destination. Our general goal is to understand how molecular chaperones overcome these challenges and ensure the proper biogenesis of membrane proteins. Our specific goal is to decipher the mechanism of a novel chaperone, cpSRP43, which ensures the targeted delivery of the most abundant membrane proteins on earth - the Light Harvesting Complex protein (LHCP) family. To this end, we will decipher the mechanism by which cpSRP43 protects the highly hydrophobic LHCPs from aggregation. We will elucidate how conformational flexibility in this chaperone enables it to coordinate its actions with the protein targeting and translocation machineries, and thus achieve the effective capture of membrane protein substrates in the aqueous phase as well as the efficient release of substrates at the target membrane. Finally, we will test whether cpSRP43 can chaperone engineered membrane protein substrates, and whether this activity allows it to improve the expression, localization, or stability of membrane proteins in vivo. Ultimately, these studies will allow us to better understand the intimate link between chaperone activity and membrane protein biogenesis, and provide a precedent for the mechanisms by which ATP-independent molecular chaperones using binding interactions to drive vectorial processes during protein localization. Exploiting the robustness and modularity of cpSRP43's activity could also lead to new and general tools to improve the production and behavior of membrane proteins.

Public Health Relevance

Biological membranes are essential for the structure, integrity, and function of all cells. The generation and maintenance of biological membranes relies critically on the proper biogenesis of the constituent membrane proteins. The proposed studies will allow us to better understand how highly aggregation-prone membrane proteins are protected from aggregation and productively delivered to the correct destination through the action of novel molecular chaperones. The results will significantly advance our understanding of the mechanism of membrane protein biogenesis, and contribute profoundly to our general understanding of physiology and pathology of all living cells at a molecular level.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM114390-02
Application #
9249613
Study Section
Biochemistry and Biophysics of Membranes Study Section (BBM)
Program Officer
Ainsztein, Alexandra M
Project Start
2016-04-01
Project End
2020-03-31
Budget Start
2017-04-01
Budget End
2018-03-31
Support Year
2
Fiscal Year
2017
Total Cost
$312,409
Indirect Cost
$93,709
Name
California Institute of Technology
Department
Type
Schools of Arts and Sciences
DUNS #
009584210
City
Pasadena
State
CA
Country
United States
Zip Code
91125
Wang, Peng; Liang, Fu-Cheng; Wittmann, Daniel et al. (2018) Chloroplast SRP43 acts as a chaperone for glutamyl-tRNA reductase, the rate-limiting enzyme in tetrapyrrole biosynthesis. Proc Natl Acad Sci U S A 115:E3588-E3596
McAvoy, Camille Z; Siegel, Alex; Piszkiewicz, Samantha et al. (2018) Two distinct sites of client protein interaction with the chaperone cpSRP43. J Biol Chem 293:8861-8873
Chandrasekar, Sowmya; Sweredoski, Michael J; Sohn, Chang Ho et al. (2017) Co-evolution of Two GTPases Enables Efficient Protein Targeting in an RNA-less Chloroplast Signal Recognition Particle Pathway. J Biol Chem 292:386-396
Chandrasekar, Sowmya; Shan, Shu-Ou (2017) Anionic Phospholipids and the Albino3 Translocase Activate Signal Recognition Particle-Receptor Interaction during Light-harvesting Chlorophyll a/b-binding Protein Targeting. J Biol Chem 292:397-406
Liang, Fu-Cheng; Kroon, Gerard; McAvoy, Camille Z et al. (2016) Conformational dynamics of a membrane protein chaperone enables spatially regulated substrate capture and release. Proc Natl Acad Sci U S A 113:E1615-24
Nguyen, Thang X; Chandrasekar, Sowmya; Neher, Saskia et al. (2011) Concerted complex assembly and GTPase activation in the chloroplast signal recognition particle. Biochemistry 50:7208-17