title: The denaturation of circular enterocin AS-48 by urea and guanidinium hydrochloride.
abstract: The unfolding thermodynamics of the circular enterocin protein AS-48, produced by Enterococcus faecalis, has been studied. The native structure of the 70-amino-acid-long protein turned out to be extremely stable against heat and denaturant-induced unfolding. At pH 2.5 and low ionic strength, it denatures at 102 degrees C, while at 25 degrees C, the structure only unfolds in 6.3 M guanidinium hydrochloride (GuHCl) and does not unfold even in 8 M urea. A comparison of its thermal unfolding in water and in the presence of urea shows a good correspondence between the two deltaGw(298) values, which are about 30 kJ mol(-1) at pH 2.5 and low ionic strength. The stability of the structure is highly dependent upon ionic strength and so GuHCl acts both as a denaturant and a stabilising agent. This seems to be why the deltaGw(298) value calculated from the unfolding data in GuHCl is twice as high as in the absence of this salt. At least part of the high stability of native AS-48 can almost certainly be put down to its circular organization since other structural features are quite normal for a protein of this size.
authors.affiliation: Departamento de Química Física e Instituto de Biotecnología, Facultad de Ciencias, Universidad de Granada, Granada, Spain.
authors.forename: Eva S
authors.initials: ES
authors.lastname: Cobos
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Filimonov
authors.forename: Antonio
authors.initials: A
authors.lastname: Gálvez
authors.forename: Eva
authors.initials: E
authors.lastname: Valdivia
authors.forename: Mercedes
authors.initials: M
authors.lastname: Maqueda
authors.forename: Jose C
authors.initials: JC
authors.lastname: Martínez
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Mateo
mesh_terms: D001430:Bacteriocins / Q000737:chemistry*; D001952:Bridged-Ring Compounds / Q000737:chemistry*; D002942:Circular Dichroism; D013293:Enterococcus faecalis / Q000378:metabolism; D019791:Guanidine; D006358:Hot Temperature; D007700:Kinetics; D008433:Mathematics; D008958:Models, Molecular; D011487:Protein Conformation; D011489:Protein Denaturation; D013816:Thermodynamics; D014508:Urea
chemical_list: D001430:Bacteriocins; D001952:Bridged-Ring Compounds; C466236:enterocin AS-48, Enterococcus faecalis; C012306:enterocin; D014508:Urea; D019791:Guanidine