title: Heightened stability of polcalcin Phl p 7 is correlated with strategic placement of apolar residues.
abstract: Phl p 7 exhibits atypical conformational stability and a diminutive denaturational heat capacity increment, ΔC(p). Because exposure of apolar surface largely dictates the magnitude of ΔC(p), a depressed value could signify an unusually compact unfolded state. The volume of the denatured state ensemble (DSE) is evidently inversely correlated with mean hydrophobicity [Pace et al., Protein Sci. 19 (2010) 929-943]. Interestingly, apolar residues replace more polar ones at four positions in Phl p 7. We herein examine the consequences of replacing those residues with the corresponding ones from Bra n 1, a related isoform. All four mutations - M4H, L21A, I60T, and C63A - destabilize Phl p 7. Our analysis suggests that the DSE of Phl p 7 is indeed highly compact and that the substitutions act by increasing its volume and solvent-accessibility. All four mutations increase the urea m value; L21A, I60T, and C63A also yield a perceptible increase in ΔC(p).
authors.affiliation: Department of Biochemistry, University of Missouri, Columbia, MO 65211, United States. henzlm@missouri.edu
authors.forename: Michael T
authors.initials: MT
authors.lastname: Henzl
authors.forename: Mark A
authors.initials: MA
authors.lastname: Reed
authors.forename: Anmin
authors.initials: A
authors.lastname: Tan
mesh_terms: D000485:Allergens / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D052179:Antigens, Plant; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D010944:Plants / Q000737:chemistry; D011058:Pollen / Q000737:chemistry; D011485:Protein Binding; D055550:Protein Stability; D058767:Protein Unfolding
chemical_list: D000485:Allergens; D052179:Antigens, Plant; D002135:Calcium-Binding Proteins; C468525:Phl p 7 allergen; D010940:Plant Proteins; D002118:Calcium