Roles of GET3B and DJA-type Stromal Chaperone Proteins in Thylakoid Targeting of Tail-anchored Proteins

Date of Award

5-2026

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Yan Lu, Ph.D.

Second Advisor

Todd Barkman, Ph.D.

Third Advisor

Silvia Rossbach, Ph.D.

Keywords

DJA, GET3B, thylakoid membrane

Access Setting

Masters Thesis-Abstract Only

Restricted to Campus until

5-1-2036

Abstract

Thylakoid membrane proteins are essential for photosynthesis. Among them, lightharvesting complex proteins (LHCPs) are targeted to thylakoid membranes via the chloroplast signal recognition particle (SRP) pathway. Unlike LHCPs, tail-anchored (TA) proteins are targeted to thylakoid membranes via the chloroplast Guided Entry of TA proteins (GET) pathway. Examples of thylakoid-targeted TA proteins include CHLOROPLAST SECRETORY TRANSLOCASE E1 (SECE1), a thylakoid-localized Sec system which is involved in importing proteins into the thylakoid membrane, and possibly Photosystem II core proteins PsbE and PsbH. One critical component of the chloroplastic GET pathway is the stromal chaperone protein GET3B, which serves as a targeting factor for this pathway. GET3B consists of an ATPase domain, a Get3 motif, a TA binding pocket, and a CXXC zinc binding motif. In addition to GET3B, the chloroplast stroma also contains heat shock protein 40 (HSP40)-type chaperone proteins (i.e., DJA4/5/6/7), each with a signature J-domain, a Gly/Phe-rich domain, and a C-terminal domain. These HSP40s are known cochaperones of heat shock protein 70 during cellular processes. Because the J-domain is known to interact with the ATPase domain, we hypothesize that DJAs may interact with GET3B and assist in the transport of thylakoid-targeted TA proteins to the thylakoid membrane. Our study showed that simultaneous mutation in the GET3B and DJA genes resulted in reduced plant growth, total chlorophyll and carotenoid content, and photosynthetic activity. This suggests a synergic interaction between GET3B and DJA. Our AlphaFold and ChimeraX analyses showed that the DJA dimer may act as a molecular clamp that holds the GET3B-TA complex during its transit into the thylakoid membrane. This study provides an understanding of chloroplast membrane protein import mechanism, which is important for photosynthesis.

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