Metal ion induced conformational transitions of prothrombin and prothrombin fragment 1

Biochemistry. 1978 Oct 17;17(21):4430-8. doi: 10.1021/bi00614a012.

Abstract

Circular dichroism experiments indicate that prothrombin fragment 1 undergoes essentially the same secondary structural change whether in the presence of Ca(2+), Mg(2+), or Mn(2+). Titration with any of these metal ions results in a sigmoidal titration curve indicative of cooperative binding. Mg(2+) and Ca(2+) have nearly identical transition midpoints, while that for Mn(2+) is an order of magnitude less. These results correlate well with the results of previous metal ion intrinsic fluorescence quenching experiments. Fragment 1 has previously been shown to undergo a second transition corresponding to dimerization at high calcium concentrations. The present circular dichroism experiments show that this transition does not result in a gross alteration of secondary structure in the fragment 1 molecule. Studies with prothrombin, similar to those with fragment 1, indicate a similar metal ion dependent conformational change but of smaller magnitude. As apparently only the fragment 1 portion of the molecule undergoes the transition, it would appear that the covalently linked fragment 1 is constrained from attaining the same conformation as the purified entity. This suggests that caution must be used in interpreting the results of metal ion binding studies using fragment 1 as an analogue for prothrombin.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium
  • Cattle
  • Circular Dichroism
  • Humans
  • Magnesium
  • Manganese
  • Peptide Fragments
  • Protein Conformation
  • Prothrombin*
  • Spectrophotometry, Ultraviolet

Substances

  • Peptide Fragments
  • Manganese
  • Prothrombin
  • Magnesium
  • Calcium