Hemoglobin Long Island is caused by a single mutation (adenine to cytosine) resulting in a failure to cleave amino-terminal methionine.

Abstract

Hemoglobin Long Island has two separate amino acid abnormalities of /3-globin structure: an extension of the NH2 terminus by a methionine residue and a histidine-toproline substitution at the normal second position. The NH2-terminal methionine residue, the translation product of an AUG initiation codon, is present only transiently in nascent proteins. Because of the general biological implications of this abnormality, we investigated the nature of the genetic defect of this mutant. We determined the sequence of the relevant portion of the f8-globin mRNA by means of dideoxynucleotide chain termination of the complementary DNA (cDNA) in which an oligonucleotide complementary to codons 10-17 was used as a primer for reverse transcriptase. A histidine-to-proline substitution was confirmed in the mutant mRNA by identifying an adenine-to-cytosine transversion in the second codon. However, we were unable to find any other abnormality at either the AUG initiation codon or in the 56 bases upstream from the adenine-to-cytosine transversion (encompassing most of the 5' untranslated region of the mutant (3-globin mRNA). Thus, it appears that this single lesion probably interferes with the poorly understood methionine-cleaving mechanism that modulates most of prokaryotic and eukaryotic proteins.We have recently described a hemoglobin mutant, hemoglobin Long Island (1), that is characterized by two separate abnormalities in the primary amino acid structure of the P3-globin chain: (i) an extension of the NH2 terminus by a methionine residue and (ii) the substitution of a proline for a histidine at the second amino acid position. A similar mutant has also been described in France as hemoglobin Marseille (2). Although more than 400 hemoglobin mutants have been described (3), this P-globin is of interest for two reasons: first, the extension of the NH2 terminus and, second, of more general biological significance, the fact that it is a mutant nonsecreted vertebrate protein in which the NH2-terminal methionine, coded by the AUG initiation codon, is preserved in the protein structure.To establish the molecular lesion responsible for this mutation, we have directly sequenced mRNA from the normal and mutant P-globin mRNA of two subjects heterozygous for Hb Long Island. The knowledge of the exact nature of the mutation associated with Hb Long Island is of interest since the protein abnormality could be caused by: (i) a general abnormality of the poorly defined methionine cleavage pathway, (ii) two separate mutations, or (iii) a single mutation that interferes with the cleavage of the initial NH2 terminus. This NH2-terminal methionine has been found to be transiently present in nascent bacterial polypeptides (4), human tumor cells in ascites fluid (5), globins (6-10), and trout cells (11). It is removed from the nascent polypeptide chain by posttranslational modification in most nonsecreted prokaryotic and eukaryotic proteins (12). Exceptions to this rule are found in various prokaryotic and eukaryotic proteins (13) and, also p...

The Action of N-terminal Acetyltransferases on Yeast Ribosomal Proteins

“…Moerschell et al (2) demonstrated antepenultimate (the third residue) proline residues can inhibit methionine cleavage from certain residues with intermediate sizes of side chains. Also, methionine cleavage was completely inhibited from the Met-Val-Pro-sequence of a mutant human hemoglobin (15,16). In other studies with Escherichia coli, antepenultimate proline residues partially inhibited cleavage from Met-Ala-Pro- (17,18) and Met-Thr-Pro- (19).…”

Nα-terminal Acetylation of Eukaryotic Proteins

“…human hemoglobin (13). In other studies with E. coli, antepenultimate proline residues partially inhibited cleavage from Met-AlaPro (4,14) and Met-Thr-Pro (15).…”

Regulated expression of microRNAs in normal and polycythemia vera erythropoiesis

“…The RNA was collected by centrifugation at 12800g for 20min at 4°C. This method yields a high purity of erythroid specific mRNAs [14].…”

“…To identify potential dysregulation of miRNAs in in vitro expanded EPs, we initially performed genomewide array profiling by CombiMatrix slides from 3 PV patients and 3 controls from days1, 14 We then set up to validate the potential differential expression of these miRNAs by qRT-PCR in 13 PV and 8 control subjects. In addition, gene expression of the miRNAs was studied at more time points of differentiation (days 1, 7, 9, 11, 14, 16, 19 and 21) and in non-expanded peripheral blood cells (i.e.…”