In pre-sterol carrier protein 2 (SCP2) in solution the leader peptide 1-20 is flexibly disordered, and residues 21-143 adopt the same globular fold as in mature SCP2

The preform of the rabbit sterol carrier protein 2 (pre-rSCP2) was cloned, the uniformly ¹⁵N-labelled protein expressed in Escherichia coli and studied by three-dimensional ¹⁵N-resolved nuclear magnetic resonance spectroscopy. In spite of its low solubility in aqueous solution of only ~ 0.3 mM, sequential ¹⁵N and ¹H backbone resonance assignments were obtained for 105 out of the 143 residues. From comparison of the sequential and medium-range nuclear Overhauser effects (NOEs) in the two proteins, all regular secondary structures previously determined in mature human SCP2 (hSCP2) were also identified in pre-rSCP2. Near-identity of the backbone ¹⁵N and ¹H chemical shifts and 1:1 correspondence of 24 long-range NOEs to backbone amide groups in the two proteins show that the residues 21-143 adopt the same globular fold in pre-rSCP2 and mature hSCP2. The N-terminal 20-residue leader peptide of pre-rSCP2 is flexibly disordered in solution and does not observably affect the conformation of the polypeptide segment 21-143.