title: 13C NMR, X-ray, and differential scanning calorimetry investigations of truncated BPTI (aprotinin) analogues.
abstract: Truncated BPTI missing residues 1 and 2 is investigated together with variants thereof (Lys-15, Arg-17, and Arg-42 are replaced by other residues in various combinations). A comparison of the X-ray structure of BPTI with that of 3-58BPTI(K15R,R17A,R42S) shows only minor variations for the backbone, but the lack of salt bridge between the terminals and the lack of two N-terminal residues provide a structure open at one end. Comparisons of amide exchange rates show a dramatic increase for the most slowly exchanging NH protons of 3-58BPTI and the analogues thereof, as compared to those of the wild-type despite only small differences in the structures. The amide exchange rates for truncated analogues increase with decreasing TTEP (temperature top endothermic peak) values. On the basis of the known structural changes comparisons to 13C chemical shifts are made. 13C chemical shifts are assigned using the D-isotope and HMBC techniques. Excellent resolution is obtained in these 1D natural abundance spectra. 13C NMR chemical shifts are shown to be able to gauge structural changes. A comparison of 13C chemical shifts of WT BPTI (aprotinin) and 3-58BPTI reveals effects caused by (i) the removal of the salt bridge of the terminii, (ii) the charge of the N-terminus, and (iii) the increased mobility of the side chain of Tyr-23. Small effects are also seen due to a conformational change of the aromatic ring of Phe-4. Ring current shifts at 13C chemical shifts are calculated. The difference in the calculated ring current effects are small comparing the wild-type with 3-58BPTI(K15R,R17A,R42S) provided the structures are relaxed. Protein unfolding as a function of pH and temperature is studied by DSC. Unfolding occurs at lower temperature with N-terminally truncated analogues, and the maximum is shifted toward higher pH.
authors.affiliation: Department of Life Sciences and Chemistry, Roskilde University, Denmark. poulerik@virgil.ruc.dk
authors.forename: P E
authors.initials: PE
authors.lastname: Hansen
authors.forename: W
authors.initials: W
authors.lastname: Zhang
authors.forename: C
authors.initials: C
authors.lastname: Lauritzen
authors.forename: S
authors.initials: S
authors.lastname: Bjørn
authors.forename: L C
authors.initials: LC
authors.lastname: Petersen
authors.forename: K
authors.initials: K
authors.lastname: Norris
authors.forename: O H
authors.initials: OH
authors.lastname: Olsen
authors.forename: C
authors.initials: C
authors.lastname: Betzel
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D007611:Aprotinin / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002247:Carbon Isotopes; D002417:Cattle; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D007611:Aprotinin