title: The human serpin proteinase inhibitor-9 self-associates at physiological temperatures.
abstract: The metastable serpin architecture is perturbed by extremes of temperature, pH, or changes in primary sequence resulting in the formation of inactive, polymeric conformations. Polymerization of a number of human serpins in vivo leads to diseases such as emphysema, thrombosis, and dementia, and in these cases mutations are present within the gene encoding the aggregating protein. Here we show that aggregation of the human serpin, proteinase inhibitor-9 (PI-9), occurs under physiological conditions, and forms aggregates that are morphologically distinct from previously characterized serpin polymers. Incubation of monomeric PI-9 at 37 degrees C leads to the rapid formation of aggregated PI-9. Using a variety of spectroscopic methods we analyzed the nature of the structures formed after incubation at 37 degrees C. Electron microscopy showed that PI-9 forms ordered circular and elongated-type aggregates, which also bind the fluorescent dye Thioflavin T. Our data show that in vitro wild-type PI-9 forms aggregates at physiological temperatures. The biological implications of PI-9 aggregates at physiological temperatures are discussed.
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, P.O. Box 13D, Clayton, Victoria 3800, Australia.
authors.forename: Lauren N
authors.initials: LN
authors.lastname: Benning
authors.forename: James C
authors.initials: JC
authors.lastname: Whisstock
authors.forename: Jiuru
authors.initials: J
authors.lastname: Sun
authors.forename: Phillip I
authors.initials: PI
authors.lastname: Bird
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Bottomley
mesh_terms: D052160:Benzothiazoles; D003704:Dementia / Q000378:metabolism; D004646:Emphysema / Q000378:metabolism; D006801:Humans; D008854:Microscopy, Electron; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000648:ultrastructure; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D015843:Serpins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013844:Thiazoles / Q000737:chemistry; D013927:Thrombosis / Q000378:metabolism
chemical_list: D052160:Benzothiazoles; D046912:Multiprotein Complexes; C102316:SERPINB9 protein, human; D015843:Serpins; D013844:Thiazoles; C009462:thioflavin T