Structural study of the glycosylated and unglycosylated forms of a genetic variant of human serum albumin (63 Asp-->Asn)

A genetic variant of human serum albumin (alloalbumin) exhibited atypical electrophoretic mobility and chromatographic behavior apparently because of the effect of a point substitution on the molecular conformation. Three forms of albumin were isolated by DEAE HPLC chromatography: normal albumin, and two variant forms V1 and V2. The point substitution (Asp-63-->Asn) generated a canonical tripeptide acceptor sequence for glycosylation with an N-linked oligosaccharide (Asn-Lys-Ser). Neuraminidase digestion followed by electrophoresis showed that the V2 variant form was glycosylated and the V1 form was not. Time-of-flight mass spectrometry yielded a molecular weight of about 2000 for the carbohydrate. Structural analysis of the carbohydrate was done by chromatographic comparison of the pyridylaminated derivatives with standards and was confirmed by proton NMR of the three pronase glycopeptides and of the pyridylaminated oligosaccharide. The oligosaccharide had a complex biantennary structure with two sialic acid residues. In normal albumin Asp-63 is exposed and is adjacent to the first disulfide bond, Cys-62-->Cys-53. The apparent effect on molecular conformation resulting in incomplete glycosylation and atypical electrophoretic mobility suggests that glycosylation may interfere with disulfide bond formation at this site.

A genetic variant of albumin (albumin Asola; Tyr140-->Cys) with no free -SH group but with an additional disulfide bridge

A 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.

Ontogeny and ultradian rhythms of adrenocorticotropin and cortisol in the late-gestation fetal horse

Fetal maturation and the timing of parturition in both sheep and primates are thought to be controlled by the hypothalamic-pituitary-adrenal axis but little is known about the endocrinology of the equine fetus. We investigated the ontogeny of plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol and corticosteroid binding capacity in the late-gestation fetal horse. We also wished to determine whether there is ultradian rhythmic release of ACTH and cortisol in fetal horses and we compared fetuses to maternal and non-pregnant adult horses. Six fetuses, 278-304 days gestation (term approximately 335), were catheterized and sampled daily until delivery. Mean (+/- S.E.M.) ACTH concentrations increased significantly from 159 +/- 21 to 246 +/- 42 pg/ml over the last 2 days before parturition. Fetal cortisol increased significantly from 3.1 +/- 1.0 to 13.4 +/- 3.7 ng/ml (mean +/- S.E.M.) over the last 9 days before delivery. The slope of regressions for ACTH and cortisol concentrations with respect to time were positive in all subjects and statistically significant in 3 of 6 for ACTH and 5 of 6 for cortisol. Fetal corticosteroid binding capacity declined from 49.5 +/- 20.5 to 16.1 +/- 2.2 ng/ml (mean +/- S.E.M.) over the last 10 days before parturition. However, the greatest changes in ACTH, cortisol and corticosteroid binding capacity occurred very late in gestation, during the last 48 to 72 h before parturition.(ABSTRACT TRUNCATED AT 250 WORDS)

The value of mentoring in nursing leadership: a descriptive study

The author of this descriptive study explores the general characteristics of mentoring relationships and their effects on professional lives as perceived by nurse administrators. An adult developmental theoretical framework was used. The sample consisted of 367, members of the California Society for Nursing Service Administrators, a group of top-level nurse administrators. The overwhelmingly positive responses supported the literature, which described a variety of significant positive developments as a result of mentoring relationships. Ninety-seven percent (n = 356) indicated changes had occurred in their lives, with a change in self-confidence indicated most frequently. More than eighty percent (n = 294) indicated the relationship was valuable. Enhancing formal and informal mentoring relationships particularly in the nursing leadership arena is important.

Analbuminemia: three cases resulting from different point mutations in the albumin gene

Analbuminemia is a very rare recessive disorder in which subjects have little or no circulating albumin, although albumin is normally the most abundant plasma protein and has many functions. Analbuminemia is caused by a variety of mutations in the albumin gene and is exhibited only by subjects homozygous for the defect. Previously the mutation had been identified at the molecular level in only two human cases; in one case it resulted from an exon-splicing defect, and in the other case it was caused by a nucleotide insertion that caused a frameshift and premature stop codon. In this investigation we identified the mutations in three unrelated subjects from different countries. In each instance a single-nucleotide mutation produced a stop codon, but the mutations occurred at three different sites: (i) in an Italian male a C-->T transition at nt 2368 in the genomic sequence of albumin, (ii) a C-->T transition at nt 4446 for an American female, and (iii) a G-->A transition at nt 7708 in a Canadian male. The size of the albumin fragment that might have been produced for the three cases varied from 31- to 213-amino acid residues, but no evidence for a circulating albumin fragment was obtained. The paradox is that analbuminemia is extremely rare (frequency < 1 x 10(6)); yet the virtual absence of albumin is tolerable despite its multiple functions.

Mentors and preceptors in the nursing profession

Mentoring and precepting are currently receiving attention in Australian nursing. Studies in private industry and corporate organizations reveal a high correlation between professional success and a positive mentoring experience. Frequently confused with preceptor relationships, mentoring differs in subtle and not-so-subtle ways. This discussion paper aims to identify differences and similarities between the various experiences in an effort to appreciate the contribution such relationships can make to the novice nurse as well as to the mentor or preceptor. Nursing can use the concepts of mentoring and precepting in a variety of ways to facilitate the transition from novice to expert as well as career changes.

Genetic variants of human serum albumin in Italy: point mutants and a carboxyl-terminal variant

Of the > 50 different genetic variants of human serum albumin (alloalbumins) that have been characterized by amino acid or DNA sequence analysis, almost half have been identified in Italy through a long-term electrophoretic survey of serum. Previously we have reported structural studies of 11 Italian alloalbumins with point mutations, 2 different carboxyl-terminal variants, and 1 case of analbuminemia in an Italian family. This article describes confirmation by DNA sequencing of mutations previously inferred from protein sequencing of 4 of the above alloalbumins; it also reports the mutations identified by protein and DNA sequence analysis of 4 other Italian alloalbumins not previously recorded: albumin Larino, His3-->Tyr; Tradate-2 (protein sequencing only), Lys225-->Gln; Caserta, Lys276-->Asn; and Bazzano, a carboxyl-terminal variant. The first 3 have point mutations that produce a single amino acid substitution, but a nucleotide deletion causes a frameshift and an altered and truncated carboxyl-terminal sequence in albumin Bazzano. In these 4 instances the expression of the alloalbumin is variable, ranging from 10% to 70% of the total albumiN, in contrast to the usual 50% each for the normal and mutant albumin. The distribution of point mutations in the albumin gene is nonrandom; most of the 47 reported point substitutions involve charged amino acid residues on the surface of the molecule that are not concerned with ligand-binding sites.

A nucleotide insertion and frameshift cause analbuminemia in an Italian family

In analbuminemia, a very rare inherited syndrome, subjects produce little or no albumin (1/100th to 1/1000th normal), presumably because of a mutation in the albumin gene; yet, they have only moderate edema and few related symptoms owing to a compensatory increase in other plasma proteins. Because of the virtual absence of albumin the defect must be identified at the DNA level. In this study the mutation causing analbuminemia in an Italian family was investigated by analysis of DNA from a mother and her daughter. The mother was homozygous for the trait and had a serum albumin value of < 0.01 g/dl (about 1/500th normal); the daughter was heterozygous for the trait and had a nearly normal albumin value. Molecular cloning and sequence analysis of DNA from both mother and daughter showed that the mutation is caused by a nucleotide insertion in exon 8; this produces a frameshift leading to a premature stop, seven codons downstream. The methods of heteroduplex hybridization and single-strand conformation polymorphism were used to compare the DNA of the mother and daughter to the DNA of two unrelated analbuminemic individuals (one Italian and one American). This showed that all three analbuminemic individuals had different mutations; these also differed from the mutation in the only human case previously studied at the DNA level, which was a splicing defect affecting the ligation of the exon 6-exon 7 sequences. Thus, analbuminemia may result from a variety of mutations and is genetically heterogeneous.

Protein and DNA sequence analysis of a 'private' genetic variant: albumin Ortonovo (Glu-505-->Lys)

Albumin Ortonovo is a slow moving variant of human serum albumin which has been found only in people coming from the small villages of Ortonovo and Nicola (Liguria, Italy) and reaches polymorphic frequency (> or = 1%) in the poorly admixed population group living in that area. This is the first report of a 'private' variant detected in a Caucasian population. It probably originated as a mutation in a founder individual many generations ago. Isoelectric focusing analysis of CNBr fragments from the purified variant localized the mutation in fragment CNBr VI (residues 447-548). This fragment was isolated on a preparative scale by reversed-phase HPLC and subjected to V8 proteinase digestion. Sequence analysis of the abnormal V8 peptide revealed that the variant arises from a previously unreported substitution at position 505 where glutamic acid has been replaced by lysine. The protein data were confirmed by DNA sequence analysis which indicated a single nucleotide change of GAA-->AAA in the corresponding codon of the structural gene. Since the amino acid substitution found in albumin Ortonovo accords with its electrophoretic mobility on cellulose acetate, residue 505 is probably exposed to the solvent. The clustering of the mutations in the intersubdomain connection linking subdomains IIIA and IIIB (residues 492-511) accords with the fact that this region lies on the molecular surface and is accessible to solvent.

Cervical manifestations of fibrosing mediastinitis: a diagnostic and therapeutic dilemma

Fibroinflammatory and fibrosclerosing lesions involving the head and neck outside the thyroid and orbit are exceedingly rare. We present two cases of fibroinflammatory and fibrosclerosing lesions originating in the mediastinum which extended superiorly to involve soft tissues of the neck. These cases indicate that a subset of fibroinflammatory and fibrosclerosing lesions found in the head and neck originate in the mediastinum.

cDNA and protein sequence of polymorphic macaque albumins that differ in bilirubin binding

The rhesus monkey, Macaca mulatta, exhibits a geographically restricted polymorphism of serum albumins Mac A and Mac B that is recognized by electrophoresis and is associated with a difference in bilirubin-binding parameters. To identify the basis of the polymorphism, the cDNA and protein sequences of serum albumin from M. mulatta were determined. Screening of a lambda gt11 rhesus liver cDNA library yielded a 1988-bp cDNA sequence that encodes the complete amino acid sequence of mature albumin, the entire propeptide, and part of the prepropeptide. Isoelectric focusing and amino-terminal protein sequencing of CNBr fragments of albumin from A/A and B/B homozygotes were performed, and the structural difference was localized to a CNBr fragment (MCB3) spanning residues 124-264. Sequence analysis of lysyl endopeptidase peptides of MCB3 established that Mac A albumin has a glutamine residue at position 188 while the Mac B albumin has a glutamic residue at the same position. PCR amplification, subcloning, and DNA sequence analysis of clones from A/A and B/B homozygotes confirmed the protein sequence data and the codon difference of CAA versus GAA, respectively. Comparison of macaque and human serum albumin shows a 93.5% identity at the amino acid level. In human serum albumin, Glu188 is located close to the IIA binding pocket for ligands, probably including bilirubin. Derivatives of coumarin compete more efficiently with bilirubin for binding sites on the Mac A albumin than on the Mac B albumin. In regions where coumarin-containing plants are important food resources, Mac B albumin may confer a selective advantage because bilirubin is less readily displaced from it.

Alloalbuminemia in Sweden: structural study and phenotypic distribution of nine albumin variants

Plasma samples exhibiting alloalbuminemia on electrophoresis at pH 8.6 were requested from clinical laboratories throughout Sweden. Nine variants, each representing a different single point mutation, were found in 100 apparently unrelated Swedes. The overall prevalence of alloalbuminemia was estimated at 1:1700. Mutations were identified by protein-structural analysis followed by allele-specific DNA hybridization to verify the most common types. Slightly retarded (+1) mobility was seen in 80 cases. Of these, 71 had the Arg(-2)----Cys proalbumin variant previously called Malmö I proalbumin. Thirteen examples of the second most frequent type, the substitution Lys313----Asn and a mobility change of -1 charge unit, were found, as well as six cases of Glu570----Lys (albumin B) and a single case of Arg-1----Gln (proalbumin Christchurch). Five previously unreported types of alloalbuminemia were identified: four instances of Glu376----Gln, which is the second known mutation at this site; two examples of Asp550----Ala, the second mutation reported at this site; and one example each of Asp63----Asn, Gln268----Arg, and Asn318----Lys. Other mutations were identified among eight subjects of foreign descent. The high frequency and relatively uniform geographic distribution of the Arg-2----Cys mutation suggest that it may have occurred in a founder individual many generation ago in Sweden.

Purification and structural study of two albumin variants in an Irish population

Two types of variant albumins were detected during routine electrophoresis on cellulose acetate on 34,000 sera from patients in a relatively stable Irish population. The fast type (IRE1) (relative mobility 1.05) had a heterozygote frequency of 1/3,780, and the slow type (IRE2) (relative mobility of 0.94) had a heterozygote frequency of 1/8,500. A method for purification of the two types of variants is described. Structural study of the fast variant established a single amino acid substitution 313 lysine----asparagine (313 Lys----Asn); this variant has been reported in several European populations and also in New Guinea indigenes. However, the slow variant has a new substitution, 479 glutamic acid----lysine (479 Glu----Lys). Because it appears to be uniquely Irish, the slow variant (formerly called IRE2) has been renamed albumin Dublin. Three other albumin variants most often reported in European populations (cumulative frequency only about 1/3,500) were not detected in this study. Because of the significance of albumin genetic variants for the study of protein evolution and as an aid in identification of drug-binding sites, clinical chemists are asked to be on the alert for cases of bisalbuminemia.

Genetic variants of serum albumin in Americans and Japanese

A collaborative search for albumin genetic variants (alloalbumins) was undertaken by cellulose acetate and agarose electrophoresis at pH 8.6 of the sera of patients at two major medical centers in the United States and of nearly 20,000 blood donors in Japan. Seventeen instances of alloalbuminemia were ascertained, and seven different alloalbumin types were characterized by structural study. Two previously unreported alloalbumin types were identified. In one type, which was present in a Caucasian family and designated Iowa City-1, aspartic acid at position 365 was replaced by valine (365 Asp----Val); this is the second reported mutation at this position. The other type present in a Japanese blood donor had the mutation 128 His----Arg. An unexpected finding was the presence in a single Japanese of a Naskapi-type alloalbumin (372 Lys----Glu), a variant that had previously been described only for certain Amerindian tribes in whom it occurs with a polymorphic frequency (greater than 1%) and in Eti Turks. An arginyl-albumin (-1 Arg, 1 Asp----Val) occurred in an American family. The other alloalbumin types identified were proalbumins Lille and Christchurch and albumin B that have a cumulative frequency of about 1:3500 in Caucasians probably because of the hypermutability of CpG dinucleotides at the mutated sites. All of the variants characterized in this study are point mutants, and the sites are spread throughout the albumin gene. However, about one-fourth of all known albumin mutations are clustered in the sequence segment from position 354 through 382.

Use of a morphologic classification to predict clinical outcome after dissection from coronary angioplasty

To determine if morphology of procedure-associated dissections could help predict clinical outcome, angiograms of 691 coronary artery dissections resulting from percutaneous transluminal coronary angioplasty were categorized according to the National Heart, Lung, and Blood Institute classification system. Classes of dissection were then correlated with clinical outcome: 543 patients with type B dissections had no increase in morbidity and mortality when compared with patients without dissection, with a similar success rate of 93.7%. Complications in this group were low and compared favorably with complication rates in procedures not associated with dissection. One hundred forty-eight procedures associated with dissections of types C to F had a significant increase in in-hospital complications, including acute closure (31%), need for emergency coronary bypass surgery (37%), myocardial infarction (13%) and repeat angioplasty (24%). The overall clinical success rate for those with types C to F dissection was 38%. The differences in clinical success and acute complications between type B and types C to F dissections were statistically significant at p less than 0.0005 for all variables studied. The angiographic morphology of a dissection during coronary angioplasty can predict clinical outcome, aiding in selection of effective therapy.

A donor splice mutation and a single-base deletion produce two carboxyl-terminal variants of human serum albumin

At least 35 allelic variants of human serum albumin have been sequenced at the protein level. All except two COOH-terminal variants, Catania and Venezia, are readily explainable as single-point substitutions. The two chain-termination variants are clustered in certain locations in Italy and are found in numerous unrelated individuals. In order to correlate the protein change in these variants with the corresponding DNA mutation, the two variant albumin genes have been cloned, sequenced, and compared to normal albumin genomic DNA. In the Catania variant, a single base deletion and subsequent frameshift leads to a shortened and altered COOH terminus. Albumin Venezia is caused by a mutation that alters the first consensus nucleotide of the 5' donor splice junction of intron 14 and the 3' end of exon 14, which is shortened from 68 to 43 base pairs. This change leads to an exon skipping event resulting in direct splicing of exon 13 to exon 15. The predicted Venezia albumin product has a truncated amino acid sequence (580 residues instead of 585), and the COOH-terminal sequence is altered after Glu-571. The variant COOH terminus ends with the dibasic sequence Arg-Lys that is apparently removed through stepwise cleavage by serum carboxypeptidase B to yield several forms of circulating albumin.

Hepatobiliary cystadenoma: a rare hepatic tumor in a child

This report describes a 3-year-old child with a hepatobiliary cystadenoma. Cystadenomas are benign, multilocular, cystic neoplasms that usually occur in middle-aged women. The patients may be asymptomatic, but often there are vague abdominal complaints related to extrinsic compression of the stomach, duodenum, or biliary tree. Recurrence following incomplete excision and the presence of carcinoma within otherwise benign cysts has been documented. Complete resection is the therapy of choice, and thorough histopathologic evaluation is imperative.

Mutations in genetic variants of human serum albumin found in Italy

A long-term electrophoretic survey of genetic variants of serum albumin has identified an alloalbumin in 589 unrelated individuals in Italy. The alloalbumins were classified electrophoretically into 17 types. The number of unrelated carriers for each type varied from 1 for several variants reported here to 103 for albumin B. The structural change in 8 of these types has previously been determined, and the amino acid substitutions in 3 additional types are reported here. Albumin Varese has a substitution, -2 arginine to histidine (-2 Arg----His), the same as that reported for proalbumin Lille; albumin Torino has the substitution 60 Glu----Lys; and albumin Vibo Valentia has the substitution 82 Glu----Lys. The ability to distinguish so many alloalbumin types by electrophoresis at several pH values indicates that similar substitutions at different sites produce variants with different electrophoretic mobilities. Except for chain terminations in two Italian variants, all the mutations thus far determined for alloalbumins are attributable to a single-base change in the structural gene, and there is a preponderance of transitions and purine mutations. Seven alloalbumins for which the structural change has been established have been ascertained only in Italy. Several of these are clustered in specific geographic regions of Italy, which suggests an origin through a founder individual. Other variants that occur worldwide are nonetheless clustered in geographic regions within Italy. In these cases an independent mutation probably occurred at a hypermutable site such as a CpG dinucleotide.

Hypermutability of CpG dinucleotides in the propeptide-encoding sequence of the human albumin gene

An electrophoretically slow albumin variant was detected with a phenotype frequency of about 1:1000 in Sweden and was also found in a family of Scottish descent from Kaikoura, New Zealand, and in five families in Tradate, Italy. Structural study established that the major variant component was arginyl-albumin, in which arginine at the -1 position of the propeptide is still attached to the processed albumin. A minor component with the amino-terminal sequence of proalbumin was also present as 3-6% of the total albumin. After amplification of the gene segment encoding the prepro sequence of albumin, specific hybridization of DNA to an oligonucleotide probe encoding cysteine at position -2 indicated the mutation of arginine at the -2 position to cysteine (-2 Arg----Cys). This produced the propeptide sequence Arg-Gly-Val-Phe-Cys-Arg. This was confirmed by sequence analysis after pyridylethylation of the cysteine. This mutation produces an alternate signal peptidase cleavage site in the variant proalbumin precursor of arginyl-albumin giving rise to two possible products, arginyl-albumin and the variant proalbumin. Another plasma from Bremen had an alloalbumin with a previously described substitution (1 Asp----Val), which also affects propeptide cleavage. Hypermutability of two CpG dinucleotides in the codons for the diarginyl sequence may account for the frequency of mutations in the propeptide. Mutation at these two sites results in a series of recurrent proalbumin variants that have arisen independently in diverse populations.

Point substitutions in Japanese alloalbumins

We have completed the structural study of five rare types of inherited albumin variants (alloalbumins) discovered in the Biochemical Genetics Study of 15,581 unrelated children in Hiroshima and Nagasaki. We have also identified the structural change in five other alloalbumin specimens detected during clinical electrophoresis of sera from Japanese living near Tokyo. Each of the five albumin variants from Nagasaki and Hiroshima has a single amino acid substitution. All of these substitutions differ, and none has been reported in non-Japanese populations. No instances of proalbumin variants or of albumin B (the most frequent alloalbumins in Caucasians) were detected in the children in Hiroshima and Nagasaki. However, one instance of a variant proalbumin and two examples of albumin B occurred in Japanese from the vicinity of Tokyo. In addition a previously unreported point substitution was found in albumin Tochigi, which is present in two unrelated persons from Tochigi prefecture. Four of the point mutations in the Japanese alloalbumins are in close proximity in a short segment of the polypeptide chain (residues 354-382) in which three additional point substitutions have been reported in diverse populations. These results, combined with earlier data, suggest that point substitutions are grouped in certain segments of the albumin molecule.

Aqueductal obstruction in sarcoidosis

A 50-year-old woman presented with a severe obstructive hydrocephalus, only temporarily relieved by shunts. The diagnosis of sarcoidosis was suspected but never proven. Autopsy revealed multisystem sarcoidosis as well as widespread involvement of the CNS. The cause of hydrocephalus was established as occlusion of the aqueduct by subependymal granulomas and massive gliosis obliterating the lumen.