title: Identification of essential amino acids in Humanin, a neuroprotective factor against Alzheimer's disease-relevant insults.
abstract: Humanin (HN) is a secretory peptide that inhibits neurotoxicity by various Alzheimer's disease-relevant insults. We have so far identified that the substitution of Leu9 for Arg nullifies the extracellular secretion of HN. Here we comprehensively investigate the amino acid requirement of HN essential for its secretion and for its neuroprotective function. Intracellulary expressed HN-EGFP (EGFP N-terminally fused with HN) was extracellularly secreted, whereas neither EGFP nor (L9R)HN-EGFP was secreted at all. While Ala substitution of neither residue affected HN secretion, Arg substitution revealed that the two structures-Leu9-Leu11 and Pro19-Va120-were essential for the secretion of full-length HN. In the Leu9-Leu11 domain, the Leu10 residue turned out to play a central role in this function, because the Asp substitution of Leu10, but not Leu9 or Leu11, nullified the secretion of HN. Utilizing Ala-scanned HN constructs, we also investigated a comprehensive structure-function relationship for the neuroprotective function of full-length HN, which revealed (i) that Pro3, Ser7, Cys8, Leu9, Leu12, Thr13, Ser14, and Pro19 were essential for this function and (ii) that Ser7 and Leu9 were essential for self-dimerization of HN. These findings indicate that HN has activity similar to a signal peptide, for which the Leu9-Leu11 region, particularly Leu10, functions as a core domain, and suggest that self-dimerization of HN is a process essential for its neuroprotective function.
authors.affiliation: Department of Pharmacology, KEIO University School of Medicine, Life Science Research Building, 6th Floor, Shinanomachi, Shinjuku-ku, Tokyo, Japan.
authors.forename: Yohichi
authors.initials: Y
authors.lastname: Yamagishi
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Hashimoto
authors.forename: Takako
authors.initials: T
authors.lastname: Niikura
authors.forename: Ikuo
authors.initials: I
authors.lastname: Nishimoto
mesh_terms: D000409:Alanine / Q000737:chemistry; D000544:Alzheimer Disease / Q000188:drug therapy / Q000378:metabolism*; D000596:Amino Acids / Q000737:chemistry; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry; D000818:Animals; D001120:Arginine / Q000737:chemistry; D017077:Culture Media, Conditioned / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D049452:Green Fluorescent Proteins; D006822:Hybrid Cells; D047908:Intracellular Signaling Peptides and Proteins; D007930:Leucine / Q000737:chemistry; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D009154:Mutation; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D018696:Neuroprotective Agents / Q000737:chemistry* / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000494:pharmacology; D051381:Rats; D013329:Structure-Activity Relationship; D013997:Time Factors; D014162:Transfection
chemical_list: D000596:Amino Acids; D016564:Amyloid beta-Protein Precursor; D017077:Culture Media, Conditioned; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D018696:Neuroprotective Agents; D010455:Peptides; D011506:Proteins; C427211:humanin; D049452:Green Fluorescent Proteins; D001120:Arginine; D007930:Leucine; D000409:Alanine