Genetic studies of low abundance human plasma proteins. II. Population genetics of coagulation factor XIIIB.

Plasma samples from a large number of different ethnic groups, consisting of U.S. whites, U.S. blacks, Eskimos from Kodiak and St. Lawrence Island, Aleuts of the Pribilof Islands, and three Amerindian groups from Canada and Mexico have been analyzed by isoelectric focusing followed by immunoblotting to determine the magnitude of genetic variation at the F XIIIB structural locus. The synthesis of published data and our new data demonstrate remarkable variation in the distribution of the three common alleles at this locus and establishes F XIIIB as an extremely informative marker for population differentiation and evolutionary studies. Genetic distance analysis based on this variation separates Caucasian, black, and Mongoloid populations into three distinct clusters.     

Genetic control of lipid transport in mice. II. Genes controlling structure of high density lipoproteins

Genetic factors controlling the structure of high density lipoproteins (HDL) in mice have been examined. Surveys of inbred strains of mice revealed genetic structural variations of the two major apolipoproteins of mouse HDL, apolipoproteins A-I and A-II. The structural variations alter the charge of the proteins as judged by isoelectric focusing of HDL under denaturing conditions. The structural variations are inherited as single Mendelian genes exhibiting co-dominant expression. The structural gene for mouse apolipoprotein A-II, designated Alp-2, resides on mouse chromosome 1, tightly linked to Ly-m20, a lymphocyte alloantigen locus. Previous studies, as well as our results, suggest that the structural gene for mouse apolipoprotein A-I, designated Alp-1, is on mouse chromosome 9. The genetic structural variation for apo-A-I results in a shift in the charge of the entire family of apo-A-I isoforms, indicating that they are all encoded by a common structural gene. The structure of intact HDL, examined primarily by electrophoretic techniques, exhibits numerous and complex phenotypes among different strains of mice. One variation, controlling the density and possibly the size of HDL, has been studied in two sets of recombinant inbred strains of mice. The results indicate that the variation is controlled by a single major gene that is either tightly linked to or identical with the Alp-2 gene on chromosome 1. In addition to structural variation, inbred strains of mice exhibited considerable quantitative variation of plasma HDL. Thus, the mouse provides a useful model system for examining the genetic control of mammalian HDL structure and regulation.     

Genetic studies of low-abundance human plasma proteins. VI. Polymorphism of hemopexin.

An analytical isoelectric focusing method in 3 M urea followed by immunoblotting has been devised to detect genetic and biochemical variation in the glycoprotein hemopexin (HPX) in human plasma or serum. HPX reveals extensive microheterogeneity with multiple major and minor components that are susceptible to neuraminidase treatment, suggesting that the observed biochemical variation is due to differences in sialic acid content between HPX isoproteins. However, charge differences that persist in HPX isoproteins following neuraminidase treatment suggest the presence of genetically determined HPX variation, and this is confirmed by population and family studies. HPX was found to be monomorphic, with an invariant pattern, in U.S. whites; but it is polymorphic in U.S. blacks, with three alleles controlled by a single locus, a situation that demonstrates an autosomal codominant pattern of inheritance. The HPX 1, HPX 2, and HPX 3 allele frequencies in U.S. blacks are .941, .018, and .041, respectively.     

Genetic studies of low-abundance human plasma proteins. XII. A new variant of corticosteroid-binding globulin detected by isoelectric focusing/immunoblotting

Thin-layer polyacrylamide gel isoelectric focusing over the pH range 3.5-5 followed by immunoblotting was used to investigate the occurrence and frequency of genetic variation in corticosteroid-binding globulin (CBG). Plasma samples from US Caucasians (n = 105) and US Blacks (n = 106) from Pittsburgh, Pa., Canadian Indians from Vancouver Island (n = 91) and Nigerian Blacks (n = 116) were analyzed. A complex isoprotein pattern was observed in all individuals tested. Reduction of this pattern to a single primary band following neuraminidase treatment indicates that the observed intraindividual variation is due to variation in the number of sialic acid residues associated with CBG. The CBG variant pattern consisted of a series of isoprotein bands having the same mobility as the common pattern, and a second series of bands at a more acidic isoelectric point. This pattern is consistent with heterozygosity for a rare CBG allele.     

Transferrin polymorphisms in Japanese populations: north-south cline in the distribution of the TF*C2 allele

Allele frequencies for human transferrin (TF) subtypes were determined using serum samples from Japanese subjects living in Fukui prefecture, Japan, and compared with other Japanese populations using isoelectric focusing (IEF) and immunoblotting. The application of IEF revealed considerable heterogeneity in the TF system, enhancing its potential value for anthropologic and genetic studies. So far, TF subtypes of about 27,000 Japanese individuals from 35 population groups have been analyzed to evaluate the degree of genetic variation at the TF locus. Possible geographic and biologic factors are discussed.     

Genetic polymorphism of alpha-2-HS-glycoprotein in a Spanish population.

The genetic polymorphism of alpha-2-HS-glycoprotein (AHSG) was analyzed in 489 unrelated individuals living in Madrid (central Spain), by isoelectric focusing in miniaturized polyacrylamide gels followed by immunoblotting. The allele frequencies were estimated to be 0.7147 and 0.2771 for AHSG*1 and AHSG*2, respectively. In addition to the common alleles, 3 rare variants (AHSG*3, AHSG*10 and AHSG*11) have been found in this study.     

Restriction isotyping of human apolipoprotein A-IV: rapid typing of known isoforms and detection of a new isoform that deletes a conserved repeat.

Genetic polymorphisms of apolipoprotein A-IV (apoA-IV) have been detected by isoelectric focusing of serum proteins. Because genetic variation in apoA-IV has significant effects on lipid risk factors, we used restriction enzyme isoform genotyping (restriction isotyping) to determine apoA-IV isoform genotypes at the DNA level for a large population (n = 509). In contrast to isoelectric focusing methods, restriction isotyping relies on nucleotide differences, enabling unambiguous typing of known isoforms and detection of new alleles that mimic other isoforms with shared charge properties. To determine genotypes for the common A-IV-1 isoform (Gln at aa position 360) and A-IV-2 isoform (360His), we used a mismatched primer for polymerase chain reaction (PCR) to introduce a restriction site (PvuII) that distinguishes each isoform. Using a portion of the same PCR reaction, we used HinfI to distinguish isoforms with Thr at position 347 (347Thr) versus Ser (347Ser). In surveys for these common genotypes, we detected heterozygotes for an allele with an insertion of 12 bp. Nucleotide sequencing showed that this allele is identical to the A-IV-0 isoform that inserts a hydrophilic repeat (Glu Gln Gln Gln) in a conserved region near the carboxy terminus. In addition, we discovered a new allele with a 12 bp deletion that removes a repeat (Glu Gln Gln Gln) from the same region. Nucleotide sequencing showed that this allele removes an acidic charge relative to A-IV-1, so we have named this isoform A-IV-2*. This isoform has not been discovered at the protein level, perhaps due to shared charge properties with A-IV-2 isoforms.     

A simple Beckman DU accessory for location of proteins separated by isoelectric focusing in granulated gel layers: Isolation of human serum very low density apolipoproteins C-II and C-III-1

A simple, low-cost gel layer scanner has been developed for the Beckman DU spectrophotometer. The gel scanner makes it possible to localize zones precisely after preparative isoelectric focusing of proteins in 2-mm thick Sephadex G-200 layers. Using the scanner after isoelectric separation of a mixture of human serum apolipoproteins C-III-1 and C-II, pure proteins could easily be obtained.     

A sensitive immunoblotting technique to identify thyroxin-binding globulin protein heterogeneity after isoelectric focusing

An enzyme-linked immunoblotting technique is described to detect thyroxin-binding globulin (TBG) variation in human plasma samples after isoelectric focusing in thin-layer polyacrylamide gels followed by transfer to a nitrocellulose membrane. The technique is used to demonstrate the polymorphic variation in thyroxin-binding globulin present in populations of African and Mongoloid origin and has enabled the detection of a new TBG variant in Eskimos. This technique eliminates the use of radioactive material and related expensive equipment. The technique is specific, sensitive, and reliable for the routine detection of genetic and epigenetic variation in thyroxin-binding globulin.This work was supported by NIH Grants RR05451-24, CA29614, and CA34836.     

Steroid receptors in human endometrium. Comparison of data obtained by three different methods

To find a method for steroid receptor measurement in small endometrial tissue samples (less than 100 mg), an isoelectric focusing assay has been compared with a dextran-coated charcoal assay for oestradiol receptor. The results correlated well (r = 0.85) and this indicates that isoelectric focusing is a good technique for oestradiol receptor determination. Te isoelectric focusing of progesterone receptor has been compared with a dextran-coated charcoal assay and sucrose density gradient centrifugation. Isoelectric focusing gave recoveries of 0-26% compared to receptor values obtained with the two other methods, which correlated well (r = 0.97). The low recovery implies that the isoelectric focusing assay is not suitable for progesterone receptor determination.     

A method to screen apolipoprotein polymorphisms in whole plasma: description of apolipoprotein A-IV variants in dyslipidemias and a reassessment of apolipoprotein A-I in Tangier disease

A sensitive and rapid immunological detection method was used to screen for apolipoprotein A-IV variants. Antibodies to human lymph chylomicron or plasma apolipoprotein A-IV, and plasma apolipoprotein A-I were raised in rabbits. Antibodies to apolipoprotein A-I or apolipoprotein A-IV were shown to be monospecific to their respective antigens by reactivity against human chylomicron apolipoproteins by immunoblot analysis. Plasma samples were obtained from dyslipidemic subjects from the Lipid Research Clinic of Columbia University. The plasma samples were isoelectrically focused (pH 4-6) on slab gels. Plasma proteins were then transferred to nitrocellulose paper for immunoblotting. Apolipoprotein A-IV polymorphism was determined by specific immunological detection of apolipoprotein A-IV. Identical apolipoprotein A-IV isoprotein patterns were observed when either antibodies to lymph or plasma apolipoprotein A-IV were used for immunoblotting. All the dyslipidemic plasma samples screened contained the two major and one or two minor isoproteins of normal plasma. In two instances, new apolipoprotein A-IV variants having an additional isoform were detected. One subject was hypertriglyceridemic (triacylglycerols = 342 mg/dl, cholesterol = 251 mg/dl) and had an additional major acidic apolipoprotein A-IV isoform. Another subject with mild hypocholesterolemia (triacylglycerols = 209 mg/dl, cholesterol = 120 mg/dl) was found to have additional major and minor basic apolipoprotein A-IV isoforms. The specificity of this technique allows detection of polymorphism of apolipoproteins of similar isoelectric points by use of a single dimension isoelectric focusing gel. This technique also demonstrated the presence of altered apolipoprotein A-I isoforms in the plasma of a patient with Tangier disease. These isoforms were previously identified as isoforms 2 and 4 of normal plasma by use of two-dimensional gel electrophoresis. However, by use of this new technique and careful evaluation of previously published two-dimensional gels, we now identify these apolipoprotein A-I isoforms as being more acidic than those of normal plasma.     

Analysis of rat serum apolipoproteins by isoelectric focusing. I. Studies on the middle molecular weight subunits.

Analytical isoelectric focusing (IEF) has been applied to the study of the apolipoprotein components of rat serum high density and very low density lipoproteins. The apolipoproteins were separated on 7.5% polyacrylamide gels containing 6.8% urea, with a pH gradient of 4-6. The middle molecular weight range apolipoproteins were identified on IEF gels by the use of apolipoproteins purified by electrophoresis on gels containing sodium dodecyl sulfate (SDS). The A-1 protein focused as 4 to 5 bands from pH 5.46 to 5.82; the A-IV protein and the arginine-rich protein each focused as 4 to 6 bands from pH 5.31 to 5.46. The low molecular weight proteins focused from pH. 4.43 to 4.83 and are the subject of a separate communication. Comparisons of the IEF method with SDS gel electrophoresis, polyacrylamide gel electrophoresis in urea, and Sephadex chromatography are also reported. Additional studies were also carried out that tend to rule out carbamylation or incomplete unfolding of the proteins in the presence of urea as the causes of the observed heterogeneity.     

A rapid micromethod for apolipoprotein E phenotyping directly in serum

A new method for the apolipoprotein E phenotyping has been developed. The method is based on isoelectric focusing of either delipidated or guanidine-HC1-treated serum or plasma in a horizontal slab gel system followed by immunoblotting using either polyclonal or monoclonal anti-apolipoprotein E antibodies as first antibody. Apolipoprotein E phenotyping with this method in 200 serum samples that had been stored at -20 degrees C for more than one year gave exactly the same results as obtained with the conventional method based on isoelectric focusing of delipidated very low density lipoproteins isolated from fresh serum followed by protein staining. Compared with the conventional method, the present method is less laborious because ultracentrifugation to isolate VLDL is not needed; it is suitable for large scale screening purposes; it needs only a few microliters of serum or plasma, and can easily be performed with samples with low concentrations of apolipoprotein E.     

Fast protein chromatofocusing of human very-low-density lipoproteins

Using fast protein chromatofocusing, a high-efficiency column chromatography method with a self-generated pH gradient and focusing effects, soluble human very-low-density lipoprotein (VLDL) apolipoproteins were fractionated between pH 6.3 and 4.0. In the presence of 6 mol/l urea and with a flow rate of 1 ml/min, one run (up to 10 mg of protein) took 30 min. VLDL apolipoproteins were separated in seven peaks. As revealed by SDS-polyacrylamide gel electrophoresis, isoelectric focusing and double-immunodiffusion against mono-specific antisera, fractions corresponded to the following proteins: apolipoprotein C-I, albumin, apolipoproteins A-I, E, C-II plus C-III0, C-III1 and C-III2, respectively. Apolipoproteins were eluted in sharp, well-resolved peaks. The recovery of proteins was 78% of the starting material. With fast protein chromatofocusing, an efficient isolation of single apolipoproteins is possible from small amounts of VLDL apolipoprotein preparations. This technique is superior to the commonly used, time-consuming methods for apolipoprotein isolation.     

Analytical techniques for cell fractions. XXI. Two-dimensional analysis of serum and tissue proteins: multiple isoelectric focusing

Two-dimensional electrophoresis, using isoelectric focusing in one dimension and electrophoresis in sodium dodecyl sulfate in the second, yields the highest resolution separation of proteins and protein subunits thus far obtained. For general research use, for genetic screening, and for clinical studies, it is important to be able to make these analyses easily, relatively rapidly, and reproducibly. This paper describes a device and methods for casting up to 20 isoelectric focusing gels in parallel, for running them in the same apparatus, and for recovering them in preparation for the second-dimension separations.     

Genetic polymorphism of human plasma apolipoprotein A-IV is due to nucleotide substitutions in the apolipoprotein A-IV gene

Genetic polymorphism of human plasma apolipoprotein A-IV has been detected by isoelectric focusing techniques followed by immunoblotting. The molecular basis for this apoA-IV polymorphism has been elucidated. Analysis of the protein coding sequences of the apoA-IV alleles 1 and 2 revealed a single G to T substitution in the apoA-IV-2 allele. The point mutation, occurring in a region highly conserved among the mouse, rat, and human A-IV apolipoproteins, converts the glutamine at position 360 of the mature protein to a histidine. This amino acid substitution adds one positive charge unit to the apoA-IV-1 isoprotein (pI 4.97) thus creating the more basic apoA-IV-2 isoprotein (pI 5.02). Computer analysis of the apoA-IV-2 allele revealed that the single G to T substitution results in the loss of a BbvI and a Fnu4HI restriction enzyme site and in the formation of a new restriction site for the enzyme SfaNI. Protein primary and secondary structure predictions were largely unaffected by this amino acid exchange. These results on the structure of the apoA-IV-1 and apoA-IV-2 alleles suggest that the three other rare isoproteins (apoA-IV-0, apoA-IV-3, and apoA-IV-4) are also due to nucleotide and subsequent amino acid substitutions in the apoA-IV sequence.     

Isolation of a major apolipoprotein of canine and murine pulmonary surfactant. Biochemical and immunochemical characteristics

We studied some of the biochemical and immunochemical properties of a major apolipoprotein in isolated pulmonary surfactant from dog and rat lungs. These apolipoproteins were purified by DEAE-cellulose chromatography in buffers containing Triton X-100. Purity of the apolipoproteins was assessed by both fused rocket and crossed immunoelectrophoreses. In addition, the apolipoproteins showed one band with an apparent molecular weight of 72 000-73 000 on SDS-polyacrylamide gel electrophoresis. These proteins are composed of two polypeptide chains of 36 000 daltons. When subjected to isoelectric focusing, the major component of the apolipoprotein had an isoelectric point of about 4.4, with very minor components near 4.6. Even though the apolipoproteins of both species had very similar amino acid compositions, including a relatively high glycine content, no immunologic cross-reactivity was observed. Rocket immunoelectrophoretic analysis of several preparations of dog and rat surfactant using the respective purified apolipoproteins as standards indicated that the apolipoprotein constituted 56.9% +/- 4.6. (S.D., n = 3) and 42.1% +/- 2.1 (S.D., n = 2) of the total protein in dog and rat surfactant, respectively.     

Some genetic implications of isoelectric focusing of human red cell phosphoglucomutase (PGM1) and serum protein group specific component (Gc): genetic diversity in the populations of Himachal Pradesh,India

For the study of group specific component (Gc) and phosphoglucomutase (PGM1) polymorphism, isoelectric focusing was performed on eleven tribal and non-tribal populations of Himachal Pradesh, India. They were chosen to illustrate interregional and intraregional variations. The subtype frequencies of these two systems showed clear differences in the genetic constitution of these populations of Himachal at both levels. There is a large increase in the mean heterozygosity (H) for each system by isoelectric focusing over that shown by electrophoresis. Discriminant and distance analyses both suggest that the subtype frequencies provide greater potential for the study of genetic diversity among populations. The data on these additional alleles found by isoelectric focusing are examined for some of their genetic and anthropological implications.     

Genetic polymorphism of alpha 2HS-glycoprotein in a French population. Description of two new rare variants

A French population was investigated for genetic polymorphism of alpha 2HS-glycoprotein (A2HS; nomenclature according to Human Gene Mapping 7, Los Angeles, 1983) using isoelectric focusing and immunoblotting. Three variants were observed together with two common alleles A2HS 1 and A2HS 2, whose frequencies were significantly different from the data in Canadians and Egyptians. An anodal variant to A2HS 1 was identical to a variant with two different nomenclatures reported by three different groups, indicating that there is a confusion in the A2HS nomenclature. The others were new variants with cathodal isoelectric points to A2HS 2 in the native state.     

Genetic studies of human apolipoproteins. XX. Genetic polymorphism of apolipoprotein J and its impact on quantitative lipid traits in normolipidemic subjects.

Apolipoprotein J (apo J) is a newly identified member of a growing family of proteins associated with various lipoprotein particles. Apo J is a glycoprotein which exists in the plasma associated with high-density lipoprotein subfractions which also contain apo A-I and cholesteryl ester transfer protein (CETP). We have investigated the possible existence of genetic polymorphism at the apo J structural locus and have evaluated its role in lipid metabolism. By employing isoelectric focusing and immunoblotting techniques, we have screened plasma or serum samples from six population groups: U.S. whites, Amerindians, Eskimos, New Guineans, U.S. blacks, and Nigerian blacks. Apo J revealed a common two-allele polymorphism only in populations with African ancestry and was found to be monomorphic in all other population groups tested. The genetic basis of the two alleles designated--APO J*1 and APO J*2, at a single structural locus, apo J-- was confirmed in a large number of segregating families. In the U.S. blacks, the frequencies of the APO J*1 and APO J*2 alleles were .76 and .24, respectively, and in the Nigerian blacks these values were .72 and .28, respectively. In addition, a single example of a rare allele designated APO J*3 was also encountered in the U.S. black sample. In Nigerian blacks, the apo J polymorphism's impact on seven quantitative lipid traits--total cholesterol, LDL-cholesterol, HDL-cholesterol, HDL3-cholesterol, HDL2-cholesterol, VLDL-cholesterol, and triglycerides--was investigated. No significant impact of the apo J polymorphism was observed for any of these lipid traits.