TMTC1 and TMTC2 are novel endoplasmic reticulum tetratricopeptide repeat-containing adapter proteins involved in calcium homeostasis.
The endoplasmic reticulum (ER) is organized in part by adapter proteins that nucleate the formation of large protein complexes. Tetratricopeptide repeats (TPR) are well studied protein structural motifs that support intermolecular protein-protein interactions. TMTC1 and TMTC2 were identified by an in silico search as TPR-containing proteins possessing N-terminal ER targeting signal sequences and multiple hydrophobic segments, suggestive of polytopic membrane proteins that are targeted to the secretory pathway. A variety of cell biological and biochemical assays was employed to demonstrate that TMTC1 and TMTC2 are both ER resident integral membrane proteins with multiple clusters of TPR domains oriented within the ER lumen. Proteomic analysis followed by co-immunoprecipitation verification found that both proteins associated with the ER calcium uptake pump SERCA2B, and TMTC2 also bound to the carbohydrate-binding chaperone calnexin. Live cell calcium measurements revealed that overexpression of either TMTC1 or TMTC2 caused a reduction of calcium released from the ER following stimulation, whereas the knockdown of TMTC1 or TMTC2 increased the stimulated calcium released. Together, these results implicate TMTC1 and TMTC2 as ER proteins involved in ER calcium homeostasis.
From the Departments of Biochemistry and Molecular Biology and Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003.
Johan C
JC
Sunryd
Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003 Veterinary and Animal Sciences.
Banyoon
B
Cheon
From the Departments of Biochemistry and Molecular Biology and Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003.
Jill B
JB
Graham
From the Departments of Biochemistry and Molecular Biology and Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003.
Kristina M
KM
Giorda
Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003 Veterinary and Animal Sciences.
Rafael A
RA
Fissore
From the Departments of Biochemistry and Molecular Biology and Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003 dhebert@biochem.umass.edu.
Daniel N
DN
Hebert
D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers; D018076:DNA, Complementary; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D057809:HEK293 Cells; D006706:Homeostasis; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction
D033942:Adaptor Proteins, Vesicular Transport; D002352:Carrier Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D008565:Membrane Proteins; C000592186:TMTC1 protein, human; C000592187:TMTC2 protein, human; D002118:Calcium
Calcium; Calcium Intracellular Release; Cell Biology; Endoplasmic Reticulum (ER); Membrane Protein