title: AFM Imaging Reveals Topographic Diversity of Wild Type and Z Variant Polymers of Human α1-Proteinase Inhibitor.
abstract: α1-Proteinase inhibitor (antitrypsin) is a canonical example of the serpin family member that binds and inhibits serine proteases. The natural metastability of serpins is crucial to carry out structural rearrangements necessary for biological activity. However, the enhanced metastability of the mutant Z variant of antitrypsin, in addition to folding defect, may substantially contribute to its polymerization, a process leading to incurable serpinopathy. The metastability also impedes structural studies on the polymers. There are no crystal structures of Z monomer or any kind of polymers larger than engineered wild type (WT) trimer. Our understanding of polymerization mechanisms is based on biochemical data using in vitro generated WT oligomers and molecular simulations. Here we applied atomic force microscopy (AFM) to compare topography of monomers, in vitro formed WT oligomers, and Z type polymers isolated from transgenic mouse liver. We found the AFM images of monomers closely resembled an antitrypsin outer shell modeled after the crystal structure. We confirmed that the Z variant demonstrated higher spontaneous propensity to dimerize than WT monomers. We also detected an unexpectedly broad range of different types of polymers with periodicity and topography depending on the applied method of polymerization. Short linear oligomers of unit arrangement similar to the Z polymers were especially abundant in heat-treated WT preparations. Long linear polymers were a prominent and unique component of liver extracts. However, the liver preparations contained also multiple types of oligomers of topographies undistinguishable from those found in WT samples polymerized with heat, low pH or guanidine hydrochloride treatments. In conclusion, we established that AFM is an excellent technique to assess morphological diversity of antitrypsin polymers, which is important for etiology of serpinopathies. These data also support previous, but controversial models of in vivo polymerization showing a surprising diversity of polymer topography.
authors.affiliation: Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.
authors.forename: Maria
authors.initials: M
authors.lastname: Gaczynska
authors.affiliation: Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.
authors.forename: Przemyslaw
authors.initials: P
authors.lastname: Karpowicz
authors.affiliation: Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, Maryland, United States of America.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Stuart
authors.affiliation: Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, Maryland, United States of America.
authors.forename: Malgorzata G
authors.initials: MG
authors.lastname: Norton
authors.affiliation: Department of Pediatrics and Biochemistry, Saint Louis University School of Medicine, Cardinal Glennon Children's Medical Center, St. Louis, Missouri, United States of America.
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Teckman
authors.affiliation: Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, Maryland, United States of America.
authors.forename: Ewa
authors.initials: E
authors.lastname: Marszal
authors.affiliation: Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.
authors.forename: Pawel A
authors.initials: PA
authors.lastname: Osmulski
mesh_terms: D001704:Biopolymers / Q000737:chemistry*; D006801:Humans; D018625:Microscopy, Atomic Force / Q000379:methods*; D000515:alpha 1-Antitrypsin / Q000737:chemistry*
chemical_list: D001704:Biopolymers; D000515:alpha 1-Antitrypsin