The solution structure and heme binding of the presequence of murine 5-aminolevulinate synthase

The mitochondrial import of 5-aminolevulinate synthase (ALAS), the first en zyme of the mammalian heme biosynthetic pathway, requires the N-terminal pr esequence. The 49 amino acid presequence transit peptide (psALAS) for murin e erythroid ALAS was chemically synthesized, and circular dichroism and H-1 nuclear magnetic resonance (NMR) spectroscopies used to determine structur al elements in trifluoroethanol/H2O solutions and micellar environments. A well defined amphipathic alpha -helix, spanning L22 to F33, was present in psALAS in 50% trifluoroethanol. Further, a short alpha -helix, defined by A 5-L8, was also apparent in the 26 amino acid N-terminus peptide, when its s tructure was determined in sodium dodecyl sulfate. Heme inhibition of ALAS mitochondrial import has been reported to be mediated through cysteine resi dues in presequence heme regulatory motifs (HRMs). A UV/visible and H-1 NMR study of hemin and psALAS indicated that a heme-peptide interaction occurs and demonstrates, for the first time, that heme interacts with the HRMs of psALAS. (C) 2001 Published by Elsevier Science B.V. on behalf of the Feder ation of European Biochemical Societies.