Cis and trans actions of the cholinesterase-like domain within the thyroglobulin dimer.
Thyroglobulin (Tg, precursor for thyroid hormone synthesis) is a large secreted glycoprotein composed of upstream regions I-II-III, followed by the approximately 570 residue cholinesterase-like (ChEL) domain. ChEL has two identified functions: 1) homodimerization, and 2) binding to I-II-III that facilitates I-II-III oxidative maturation required for intracellular protein transport. Like its homologs in the acetylcholinesterase (AChE) family, ChEL possesses two carboxyl-terminal alpha-helices. We find that a Tg-AChE chimera (swapping AChE in place of ChEL) allows for dimerization with monomeric AChE, proving exposure of the carboxyl-terminal helices within the larger context of Tg. Further, we establish that perturbing trans-helical interaction blocks homodimerization of the Tg ChEL domain. Additionally, ChEL can associate with neuroligins (a related family of cholinesterase-like proteins), demonstrating potential for Tg cross-dimerization between non-identical partners. Indeed, when mutant rdw-Tg (Tg-G2298R, defective for protein secretion) is co-expressed with wild-type Tg, the two proteins cross-dimerize and secretion of rdw-Tg is partially restored. Moreover, we find that AChE and soluble neuroligins also can bind to the upstream Tg regions I-II-III; however, they cannot rescue secretion, because they cannot facilitate oxidative maturation of I-II-III. These data suggest that specific properties of distinct Tg ChEL mutants may result in distinct patterns of Tg monomer folding, cross-dimerization with wild-type Tg, and variable secretion behavior in heterozygous patients.
Wang
Xiaofan
X
Division of Metabolism, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0678, USA.
Lee
Jaemin
J
Di Jeso
Bruno
B
Treglia
A Sonia
AS
Comoletti
Davide
D
Dubi
Noga
N
Taylor
Palmer
P
Arvan
Peter
P
D000110:Acetylcholinesterase / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D015816:Cell Adhesion Molecules, Neuronal / Q000737:chemistry; D002802:Cholinesterases / Q000737:chemistry*; D019281:Dimerization; D006579:Heterozygote; D006801:Humans; D051379:Mice; D018832:Molecular Chaperones / Q000737:chemistry; D009154:Mutation; D018384:Oxidative Stress; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013954:Thyroglobulin / Q000737:chemistry*
D015816:Cell Adhesion Molecules, Neuronal; D018832:Molecular Chaperones; D011993:Recombinant Fusion Proteins; C093438:neuroligin 1; D013954:Thyroglobulin; D000110:Acetylcholinesterase; D002802:Cholinesterases