title: The role of Thr5 in human neuron growth inhibitory factor.
abstract: GIF, a member of the metallothionein (MT) family (assigned as MT3), is a neuron growth inhibitory factor that inhibits neuron outgrowth in Alzheimer's disease. The conserved Thr5 is one of the main differences between GIF and other members in the MT family. However, natural sheep GIF has an unusual Ala5, casting doubt on the role of common Thr5. We constructed a series of human GIF mutants at site 5, and characterized their biochemical properties by UV spectroscopy, circular dichroism spectroscopy, EDTA reaction, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) reaction, and pH titration. Their inhibitory activity toward neuron survival and neurite extension was also examined. Interestingly, the T5A mutant exhibited distinct metal thiolate activity in the EDTA and DTNB reactions, and also lost its bioactivity. Meanwhile, the T5S mutant had similar biochemical properties and biological activity as wild-type human GIF, indicating the hydroxyl group on the Thr5 was critical to the bioactivity of human GIF. We suggest the hydroxyl group in human GIF may help stabilize the biologically active conformation. On the other hand, lack of the hydroxyl group in sheep GIF may be partially compensated by its abnormal structure.
authors.affiliation: Chemical Biology Laboratory, Department of Chemistry, Fudan University, 200433 Shanghai, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Cai
authors.forename: Qi
authors.initials: Q
authors.lastname: Zheng
authors.forename: Xin-Chen
authors.initials: XC
authors.lastname: Teng
authors.forename: Dong
authors.initials: D
authors.lastname: Chen
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.forename: Ke-Qiang
authors.initials: KQ
authors.lastname: Wang
authors.forename: Guo-Ming
authors.initials: GM
authors.lastname: Zhou
authors.forename: Yi
authors.initials: Y
authors.lastname: Xie
authors.forename: Ming-Jie
authors.initials: MJ
authors.lastname: Zhang
authors.forename: Hong-Zhe
authors.initials: HZ
authors.lastname: Sun
authors.forename: Zhong-Xian
authors.initials: ZX
authors.lastname: Huang
mesh_terms: D000818:Animals; D001483:Base Sequence; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002942:Circular Dichroism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D017665:Hydroxyl Radical / Q000737:chemistry / Q000378:metabolism; D013058:Mass Spectrometry; D008668:Metallothionein / Q000737:chemistry / Q000378:metabolism; D000090023:Metallothionein 3; D050505:Mutant Proteins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D016501:Neurites / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D013912:Threonine / Q000235:genetics / Q000502:physiology
chemical_list: D000090023:Metallothionein 3; D050505:Mutant Proteins; D009419:Nerve Tissue Proteins; D013912:Threonine; D017665:Hydroxyl Radical; D008668:Metallothionein