title: Double thermal transitions of type I collagen in acidic solution.
abstract: Contributed equally to this work. To further understand the origin of the double thermal transitions of collagen in acidic solution induced by heating, the denaturation of acidic soluble collagen was investigated by micro-differential scanning calorimeter (micro-DSC), circular dichroism (CD), dynamic laser light scattering (DLLS), transmission electron microscopy (TEM), and two-dimensional (2D) synchronous fluorescence spectrum. Micro-DSC experiments revealed that the collagen exhibited double thermal transitions, which were located within 31-37 °C (minor thermal transition, T(s) ∼ 33 °C) and 37-55 °C (major thermal transition, T(m) ∼ 40 °C), respectively. The CD spectra suggested that the thermal denaturation of collagen resulted in transition from polyproline II type structure to unordered structure. The DLLS results showed that there were mainly two kinds of collagen fibrillar aggregates with different sizes in acidic solution and the larger fibrillar aggregates (T(p2) = 40 °C) had better heat resistance than the smaller one (T(p1) = 33 °C). TEM revealed that the depolymerization of collagen fibrils occurred and the periodic cross-striations of collagen gradually disappeared with increasing temperature. The 2D fluorescence correlation spectra were also applied to investigate the thermal responses of tyrosine and phenylalanine residues at the molecular level. Finally, we could draw the conclusion that (1) the minor thermal transition was mainly due to the defibrillation of the smaller collagen fibrillar aggregates and the unfolding of a little part of triple helices; (2) the major thermal transition primarily arose from the defibrillation of the larger collagen fibrillar aggregates and the complete denaturation of the majority part of triple helices.
authors.affiliation: Department of Biomaterials & Artificial Organs, Institute of Biomedical Engineering, Chinese Academy of Medical Science & Peking Union Medical College, Key Laboratory of Biomedical Material of Tianjin, Tianjin 300192, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.forename: Lingrong
authors.initials: L
authors.lastname: Liu
authors.forename: Mingmao
authors.initials: M
authors.lastname: Chen
authors.forename: Qiqing
authors.initials: Q
authors.lastname: Zhang
mesh_terms: D000818:Animals; D002152:Calorimetry, Differential Scanning; D002417:Cattle; D002942:Circular Dichroism; D024042:Collagen Type I / Q000737:chemistry* / Q000648:ultrastructure; D006863:Hydrogen-Ion Concentration; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D024042:Collagen Type I; D012996:Solutions