933 research outputs found
Binding of warfarin, salicylate, and diazepam to genetic variants of human serum albumin with known mutations.
No full textPossible effects of single point mutations on the ligand-binding capabilities of human serum albumin (Alb) were investigated by studying the interactions between the strongly bound drugs warfarin, salicylate, and diazepam and five structurally characterized genetic variants of the protein. Equilibrium dialysis data, obtained with the variants and normal serum Alb, revealed pronounced reductions in high affinity binding of all three ligands to Alb Canterbury (313 Lys----Asn) and to Alb Parklands (365 Asp----His). By contrast, unchanged binding of the drugs was found in the case of Alb Verona (570 Glu----Lys). Different effects on binding were observed for the other two variants. Salicylate was the only drug bound with a lower affinity to Alb Niigata (269 Asp----Gly), whereas binding of both salicylate and diazepam to Alb Roma (321 Glu----Lys) were moderately reduced. In about half of the cases of diminished binding, the primary association constant was reduced by 1 order of magnitude, giving rise to an increase in the unbound fraction of the drugs of 500% or more at therapeutically relevant molar ratios of drug and protein. Changes in protein charge seem to be of only minor importance for reduced binding. More likely, conformational changes in the 313-365 region of the proteins are the main cause for diminished binding of these diverse ligands, which probably have different high affinity binding sites. The specific reduction in salicylate binding after modification of residue 269 may be due to conformational changes at or close to the salicylate binding site
MODIFIED HIGH_AFFINITY BINDING OF NICKEL; CALCIUM AND ZINC TO NATURAL MUTANTS OF HUMAN SERUM ALBUMIN AND PROALBUMIN
No full textHormone binding to natural mutants of human serum albumin.
No full textHigh-affinity binding of progesterone, testosterone, prostaglandin F2 alpha and L-thyroxine to five genetic variants of human serum albumin with defined point mutations was investigated by equilibrium dialysis (pH 7.4). Endogenous albumin A (Alb A) from each individual and commercial human serum albumin were used as controls in each case. The association constant for binding of progesterone to Alb Canterbury (Lys313----Asn) was 1.5 times that calculated for binding to the corresponding, endogenous Alb A. In contrast, the variants Alb Niigata (Asp269----Gly), Alb Roma (Glu321----Lys), Alb Parklands (Asp365----His) and Alb Verona (Glu570----Lys) all had normal progesterone binding properties. Specificity with respect to the type of mutation was also found for the binding of testosterone and prostaglandin F 2 alpha. Testosterone binding to Alb Roma was only 0.7 of that determined for endogenous Alb A, whereas prostaglandin F 2 alpha binding to Alb Niigata was increased by a factor 2.4. In the case of L-thyroxine normal binding properties were found for all the variants. Steric effects and/or conformational changes of the protein, introduced by the amino acid substitutions, probably account for the altered hormone binding. However, in the case of the increased binding of prostaglandin F2 alpha to Alb Niigata electrostatic effects could also be involved. The experimental findings suggest different high-affinity sites for the four hormones. Progesterone, testosterone and prostaglandin F2 alpha are apparently bound within the middle third (domain II) of the protein molecule. The possible position of the primary L-thyroxine site is discusse
High-affinity binding of warfarin, salicylate and diazepam to natural mutants of human serum albumin modified in the C-terminal end.
No full textHigh-affinity binding of warfarin, salicylate and diazepam to four natural mutants of human serum albumin was studied by equilibrium dialysis at pH 7.4. The mutants Alb Milano Fast and Alb Vanves possess single amino acid substitutions close to the C-terminus, namely 573 Lys-->Glu and 574 Lys-->Asn, respectively. By contrast, Alb Catania and Alb Venezia are chain termination mutants in which several amino acids have been changed or deleted. Binding of warfarin to the variants was lower than binding to normal (wild-type) albumin (Alb A). The association constants were 73% (Alb Milano Fast, Alb Vanves and Alb Catania) or 67% (Alb Venezia) of that determined for Alb A. The results obtained with salicylate were more dependent on the type of mutation. The constants were either comparable to the normal value (Alb Catania) or reduced to 64% (Alb Milano Fast), 71% (Alb Vanves) or 43% (Alb Venezia) of that value. Diazepam binding to the variants was normal, except for binding to Alb Venezia in which case the association constant was reduced to 76% of that calculated for Alb A. The results are in accordance with the view that warfarin, salicylate and diazepam bind to three different high-affinity sites. It is proposed that the sites for warfarin and salicylate are situated rather close to each other in domain II, and that these high-affinity sites are relatively susceptible to conformational changes of the protein. By contrast, the primary diazepam site is placed closer to, or within, domain III of albumin and seems to be less affected by conformational changes in the protein molecule
Human serum albumin isoforms: genetic and molecular aspects and functional consequences.
No full textBACKGROUND:
At present, 67 different genetic variants of human serum albumin and proalbumin have been molecularly characterized at the protein and/or gene level.
SCOPE OF REVIEW:
This review summarizes present knowledge about genetic and molecular aspects, functional consequences and potential uses of the variants.
MAJOR CONCLUSIONS:
The frequency of bisalbuminemia in the general population is probably about 1:1000, but it can be much higher in isolated populations. Mutations are often due to hypermutable CpG dinucleotides, and in addition to single-amino acid substitutions, glycosylated variants and C-terminally modified alloalbumins have been found. Some mutants show altered stability in vivo and/or in vitro. High-affinity binding of Ni(++) and Cu(++) is blocked, or almost so, by amino acid changes at the N-terminus. In contrast, substitution of Leu90 and Arg242 leads to strong binding of triiodothyronine and l-thyroxine, respectively, resulting in two clinically important syndromes. Variants often have modified plasma half-lives and organ uptakes when studied in mice.
GENERAL SIGNIFICANCE:
Because alloalbumins do not seem to be associated with disease, they can be used as markers of migration and provide a model for study of neutral molecular evolution. They can also give valuable molecular information about albumins binding sites, antioxidant and enzymatic properties, as well as stability. Mutants with increased affinity for endogenous or exogenous ligands could be therapeutically relevant as antidotes, both for in vivo and extracorporeal treatment. Variants with modified biodistribution could be used for drug targeting. In most cases, the desired function can be further elaborated by producing site-directed, recombinant mutants. This article is part of a Special Issue entitled Serum Albumin
MUTATIONS IN THE GENE OF HUMAN SERUM ALBUMIN: MOLECULAR AND FUNCTIONAL CONSEQUENCES AND THERAPEUTIC POSSIBILITIES
No full textCongenital analbuminaemia: molecular defects and biochemical and clinical aspects.
No full textBACKGROUND:
DNA and mRNA sequencing of the coding regions of the human albumin gene (ALB) and of its intron/exon junctions has revealed twenty-one different molecular defects causing congenital analbuminaemia (CAA).
SCOPE OF REVIEW:
To describe the mutations in molecular terms and to present the current knowledge about the most important biochemical and clinical effects of CAA.
MAJOR CONCLUSIONS:
CAA is rare, but its frequency seems to be significantly higher in restricted and minimally admixed populations. The condition affects especially the lipid metabolism but apart from a possible increased risk for atherosclerotic complications, it is generally associated with mild clinical symptoms in adults. By contrast, several reports indicate that analbuminaemic individuals may be at risk during the perinatal and childhood periods, in which they seem to show increased morbidity and mortality. The twenty-one causative defects include seven nonsense mutations, seven changes affecting splicing, five frame-shift/deletions, one frame-shift/insertion and one mutation in the start codon. These results indicate that the trait is an allelic heterogeneous disorder caused by homozygous (nineteen cases) or compound heterozygous (single case) inheritance of defects. Most mutations are unique, but one, named Kayseri, is responsible for about half of the known cases.
GENERAL SIGNIFICANCE:
Study of the defects in the ALB resulting in CAA allows the identification of "hot spot" regions and contributes to understanding the molecular mechanism underlying the trait. Such studies could also give molecular information about different aspects of ALB regulation and shed light on the regulatory mechanisms involved in the synthesis of the protein. This article is part of a Special Issue entitled Serum Albumin
A genetic variant of albumin (albumin Asola; Tyr140-->Cys) with no free -SH group but with an additional disulfide bridge.
No full textA slow migrating variant of human serum albumin, present in lower amount than the normal protein, has been detected by routine clinical electrophoresis at pH 8.6 in two members of a family living in Asola (Lombardia, Italy). Ion-exchange chromatography of serum samples failed to separate the normal protein from the variant. Analysis of the albumin peak by SDS/PAGE revealed that the variant had a lower apparent molecular mass than its normal counterpart. However, the abnormal band was not detectable when the separation was performed under reducing conditions or when both albumins were carboxymethylated. Isoelectric-focusing analysis of CNBr fragments localized the mutation to fragment CNBr 3 (residues 124-298). This fragment was isolated on a preparative scale and subjected to tryptic digestion. Sequence determination of the abnormal tryptic peptide revealed that the variant arises from a Tyr140--> Cys substitution. This result was confirmed by DNA sequence analysis, which showed a single transition of TAT-->TGT at nucleotide position 5074. Despite the presence of an additional cysteine residue, several lines of evidence indicated that albumin Asola has no free -SH group; therefore, we propose the formation of a new S-S bond between Cys140 and Cys34, the only free sulphydryl group present in the normal protein. The relatively low level of the variant in serum and its abnormal mobility on cellulose acetate electrophoresis and SDS/PAGE are probably caused by a gross conformational change of the molecule induced by the new S-S bridge
Structural characterization and fatty acid binding properties of two French genetic variants of human serum albumin.
No full textStructural characterization of three genetic variants of human serum albumin modified in subdomains IIB and IIIA.
No full textThree new genetic variants of human serum albumin have been detected in Italy by routine clinical electrophoresis. Albumin Milano Slow is common in Northern Italy, while albumins Liprizzi and Trieste, which are fast migrating, are rare and local variants. Isoelectric focusing analysis of the CNBr fragments obtained from the carboxymethylated alloalbumins in all cases localized the mutation to fragment CB5 (residues 330-446). The modified CNBr fragments were isolated on a preparative scale and subjected to tryptic digestion. Sequence determination of the abnormal tryptic peptides revealed that all the variants are caused by single point mutations: Trieste, Lys359-->Asn, Milano Slow, Asp375-->His, and Liprizzi, Arg410-->Cys. These results were confirmed by sequence determination of a variant V8 peptide in the case of Trieste, and by DNA sequence analysis for the other two variants. The DNA analysis showed a G-->C transversion at nucleotide position 11969 for albumin Milano Slow, and a C-->T transition at position 13251 for Liprizzi. The latter represents a mutation at a hypermutable CpG dinucleotide site. Albumins Trieste and Milano Slow, as most of the variants thus far described, have mutations involving residues on the surface of the molecule. In contrast, albumin Liprizzi represents the first example of a mutation in the most active binding pocket of the molecule, placed in subdomain IIIA
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