Human transferrins C and D-Chi: an amino acid difference

Application of capillary isoelectric focusing and peptide mass fingerprinting in carbohydrate-deficient transferrin detection

Carbohydrate-deficient transferrin (CDT) is a specific biomarker of alcohol abuse and is widely used in clinical diagnosis to detect and follow up excessive alcohol consumption. However, false %CDT results still exist in CDT detection, because of interference from genetic variants and the lack of standardization in CDT analysis. Therefore, it is still very important to find a method with high sensitivity and high accuracy for CDT detection. Here, we compared the detection sensitivity and accuracy of pI values based methods [isoelectric focusing on polyacrylamide gel electrophoresis (IEF-PAGE) and capillary isoelectric focusing (CIEF)] with hydrophobic characteristic based methods [reversed-phase high-performance liquid chromatography (RP-HPLC)] on CDT detection. Moreover, we investigated the potential of peptide mass fingerprinting (PMF), a method based on the mass spectrometry to identify human transferrin (HTf) variants including CDT isoforms and genetic variants, based on their specific peptide masses. Results indicated that PMF can identify HTf variants including CDT isoforms and genetic variants based on their specific peptides, and CIEF showed higher sensitivity detection of HTf variants than RP-HPLC and IEF-PAGE did. Accordingly, we suggest that PMF is suitable for identifying CDT with high accuracy, and CIEF has potential for detection of CDT and genetic variants with high sensitivity; moreover, they are both worth further investigation in clinical diagnosis.

Genotyping of TF*Dchi allele in human transferrin polymorphism

Transferrin (TF) polymorphism, one of the most useful genetic markers, have been studied extensively. TF*Dchi allele is widely distributed both among east Asian populations and American Indian populations. The TFDchi peptide was characterized by replacement of His by Arg at position 300 by amino acid sequencing. In the present study, one base substitution at the 956th nucleotide from the first nucleotide in the starting codon that induced His300Arg exchange was confirmed by direct DNA sequencing. The genotyping method used to detect the TF*Dchi allele involved the use of PCR-RFLP and restriction enzyme Acc II. Analysis of the 1765th nucleotide, which determines the common TF alleles, TF*C1 and TF*C2, in TF*Dchi cDNA indicated that the TF*Dchi allele is derived from the TF*C1 allele.

A comparison of the structure and properties of normal human transferrin and a genetic variant of human transferrin

1. A rare genetic variant of human serum transferrin (TfBSHAW) is reported. 2. The variant and normal transferrins have been purified. 3. The two proteins have been shown to be identical with respect to their molecular weights, heat stability, iron uptake and absorbance spectra. 4. The amino acid substitution is thought to be isoleucine replaced by asparagine at either position 378 or position 381. 5. The ferric iron bound to the C-site of TfBSHAW is unstable in the presence of protons or 6 M urea.

Human transferrin: cDNA characterization and chromosomal localization

Transferrin (Tf) is the major iron binding protein in vertebrate serum. It shares homologous amino acid sequences with four other proteins: lactotransferrin, ovotransferrin, melanoma antigen p97, and HuBlym-1. Antigen p97 and the Tf receptor genes have been mapped on human chromosome 3. The goal of the study described here was to initiate the characterization of the Tf gene by identifying and characterizing its cDNA and mapping its chromosomal location. Recombinant plasmids containing human cDNA encoding Tf have been isolated by screening an adult human liver library with a mixed oligonucleotide probe. Within the 2.3 kilobase pairs of Tf cDNA analyzed, there is a probable leader sequence encoded by 57 nucleotides followed by 2037 nucleotides that encode the homologous amino and carboxyl domains. During evolution, three areas of the homologous amino and carboxyl domains have been strongly conserved, possibly reflecting functional constraints associated with iron binding. Chromosomal mapping by in situ hybridization and somatic cell hybrid analysis indicate that the Tf gene is located at q21-25 on human chromosome 3, consistent with linkage of the Tf, Tf receptor, and melanoma p97 loci.

Review of isoelectric focusing for Gc, PGM1, Tf, and Pi subtypes: population distributions

Isoelectric focusing (IEF) as a method for differentiating macromolecules with minor differences in isoelectric points has demonstrated an increase in the degree of genetic polymorphisms of the blood. Studies over the last 5 to 6 years have shown that genetic marker systems such as transferrin (TF), phosphoglucomutase (PGM1), the vitamin D-binding globulin (GC), and A1 antitrypsin (PI) are a great deal more polymorphic than observed using conventional electrophoresis. Additional genetic variants have been detected or further defined in such systems as esterase D (ESD) and hemoglobin (HB) to name a few. The increased heterozygosity levels of these genetic marker systems identified by IEF have added to their value in forensic medicine and resulted in further resolution of racial and population affinities. IEF should prove to be a valuable anthropological tool for measuring population structure and genetic distances.

The complete amino acid sequence of human serum transferrin

The complete amino acid sequence of human serum transferrin has been determined by aligning the structures of the 10 CNBr fragments. The order of these fragments in the polypeptide chain is deduced from the structures of peptides overlapping methionine residues and other evidence. Human transferrin contains 678 amino acid residues and--including the two asparagine-linked glycans--has an overall molecular weight of 79,550. The polypeptide chain contains two homologous domains consisting of residues 1-336 and 337-678, in which 40% of the residues are identical when aligned by inserting gaps at appropriate positions. Disulfide bond arrangements indicate that there are seven residues between the last half-cystine in the first domain and the first half-cystine in the second domain and therefore, a maximum of seven residues in the region of polypeptide between the two domains. Transferrin--which contains two Fe-binding sites--has clearly evolved by the contiguous duplication of the structural gene for an ancestral protein that had a single Fe-binding site and contained approximately 340 amino acid residues. The two domains show some interesting differences including the presence of both N-linked glycan moieties in the COOH-terminal domain at positions 413 and 610 and the presence of more disulfide bonds in the COOH-terminal domain (11 compared to 8). The locations of residues that may function in Fe-binding are discussed.

The amino-acid sequences of three cystine-free cyanogen-bromide fragments of human serum transferrin

The amino acid sequences of three fragments obtained on cyanogen bromide cleavage of human transferrin have been determined. Two of the fragments are small (4 and 7 residues) and had not been isolated in previous studies of the CNBr fragments of transferrin. The sequence of the larger fragment (53 residues) was elucidated by examining peptides isolated from digests of the fragment with trypsin, chymotrypsin or thermolysin. This region of transferrin appears to contain the sites of three previously-reported substitutions in the D1 and D-chi genetic variants.

The world distribution of transferrin variants and some unsolved problems

Nineteen variants of the iron-binding protein, transferrin, have been described in human serum. The world literature on the distribution of these variants in human populations is surveyed in comprehensive tables and attention is drawn to some of the outstanding deficiencies in our present knowledge of this distribution. It is pointed out that transferrin variants are important markers in anthropological studies.

Transferrin D1: identity in Australian aborigines and American Negroes

Human transferrin D(1) obtained from an Australian aborigine was found to have the same substitution of glycine for aspartic acid in peptide 1C previously shown in transferrin D(1) from an American Negro. This finding is relevant to formation of distinct Australoid and African populations.