© 2007 The Japanese Biochemical Society.
Characteristics of Type IV Collagen Unfolding Under Various pH Conditions as a Model of Pathological Disorder in Tissue
1Department of Environmental Engineering for Symbiosis, Faculty of Engineering, Soka University; 2Cancer Screening Technology Division Research Center For Prevention and Screening, National Cancer Center; and 3Department of Pathology, Nippon Medical School, Tokyo, Japan
*To whom correspondence should be addressed. Tel: +81-426-91-2317, Fax: +81-426-91-2317, E-mail: shimizu{at}t.soka.ac.jp
Received February 17, 2007; Accepted April 11, 2007
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Abstract |
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The overall structure of type IV collagen is the same at neutral and acidic pH, as determined by circular dichroism spectra. The heating rate dependence of denaturation midpoint temperature (Tm) shows that type IV collagen is unstable at body temperature, similarly to type I collagen. The heating rate dependence of Tm at neutral pH has two phases, but that at acidic pH apparently has a single phase. The Tm of the first phase (lower Tm) at neutral pH is consistent with that at acidic pH, and the activation energy of these phases is consistent, within experimental error. The triple helix region of type IV collagen corresponding to the second phase (higher Tm) at neutral pH is thermally stable when compared to the triple helical structure at acidic pH. At acidic pH, as the loosely packed and unstable region has spread throughout the whole molecule, the thermal transition is thought to be cooperative and is observed as a single phase. Structural flexibility is related to protein function and assembly; therefore, the unstable structure and increased flexibility of type IV collagen induced at acidic pH may affect diseases accompanied by type IV collagen disorder.
Key Words: collagen type IV, effect of solution pH, thermal unfolding
Abbreviations: UV, ultraviolet; CD, circular dichroism; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis