title: Spontaneous thioester bond formation in alpha 2-macroglobulin, C3 and C4.
abstract: Purified alpha 2-macroglobulin and complement proteins C3 and C4 were treated with ammonia to break their intramolecular thioester bonds and reform the original free cysteinyl and glutamyl side chains. When this reaction was performed at low temperature a conformational intermediate was trapped which lacked a thioester, but which could refold to the native structure and spontaneously reform the thioester and full biological function. The findings suggest that these proteins may undergo spontaneous post-translational self-modification forming the thioesters without involvement of enzymes or high energy metabolites such as ATP.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, Tyler 75710.
authors.forename: M K
authors.initials: MK
authors.lastname: Pangburn
mesh_terms: D003176:Complement C3 / Q000737:chemistry*; D003181:Complement C4 / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry; D004952:Esters / Q000737:chemistry; D005971:Glutamates / Q000737:chemistry; D018698:Glutamic Acid; D006358:Hot Temperature; D006801:Humans; D011487:Protein Conformation; D013438:Sulfhydryl Compounds / Q000737:chemistry; D000511:alpha-Macroglobulins / Q000737:chemistry*
chemical_list: D003176:Complement C3; D003181:Complement C4; D004952:Esters; D005971:Glutamates; D013438:Sulfhydryl Compounds; D000511:alpha-Macroglobulins; D018698:Glutamic Acid; D003545:Cysteine