The three-dimensional structure of human serum albumin has been determined crystallographically to a resolution of 2.8 A. It comprises three homologous domains that assemble to form a heart-shaped molecule. Each domain is a product of two subdomains that possess common structural motifs. The principal regions of ligand binding to human serum albumin are located in hydrophobic cavities in subdomains IIA and IIIA, which exhibit similar chemistry. The structure explains numerous physical phenomena and should provide insight into future pharmacokinetic and genetically engineered therapeutic applications of serum albumin.

Atomic structure and chemistry of human serum albumin.

CNS stem cells express a new class of intermediate filament protein.

Publisher Summary This chapter provides an insight of the findings of past significant papers with the current knowledge of the recently determined high resolution X-ray structure of serum albumin. The most outstanding property of albumin is its ability to bind reversibly an incredible variety of ligands. The sequences of all albumins are characterized by a unique arrangement of disulfide double loops that repeat as a series of triplets. Albumin belongs to a multigene family of proteins that includes α- fetoprotein (AFP) and vitamin D-binding protein (VDP), also known as G complement (Gc) protein. Although AFP is considered the fetal counterpart of albumin, its binding properties are distinct and it is suggested that AFP may have a higher affinity for some unknown ligands important for fetal development. Domain structure and the arrangement of the disulfides, the surface charge distribution, and the conformational flexibility of the albumin molecule are described. The nature of ligand binding, including small organics, long-chain fatty acids, and metals, to multiple sites on the albumin molecule is clearly depicted. The chapter concludes with the perceptive comments on future directions being taken to explore the structure and function of this fascinating protein.

Structure of serum albumin.

According to the signal hypothesis, a signal sequence, once having initiated export of a growing protein chain across the rough endoplasmic reticulum, is cleaved from the mature protein at a specific site. It has long been known that some part of the cleavage specificity resides in the last residue of the signal sequence, which invariably is one with a small, uncharged side-chain, but no further specific patterns of amino acids near the point of cleavage have been discovered so far. In this paper, some such patterns, based on a sample of 78 eukaryotic signal sequences, are presented and discussed, and a first attempt at formulating rules for the prediction of cleavage sites is made.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1983.tb07424.x

Patterns of Amino Acids near Signal‐Sequence Cleavage Sites

Full length cDNAs encoding the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from rat and man have been isolated and sequenced. Many GAPDH gene-related sequences have been found in both genomes based on genomic blot hybridization analysis. Only one functional gene product is known. Results from genomic library screenings suggest that there are 300-400 copies of these sequences in the rat genome and approximately 100 in the human genome. Some of these related sequences have been shown to be processed pseudogenes. We have isolated several rat cDNA clones corresponding to these pseudogenes indicating that some pseudogenes are transcribed. Rat and human cDNAs are 89% homologous in the coding region, and 76% homologous in the first 100 base pairs of the 3'-noncoding region. Comparison of these two cDNA sequences with those of the chicken, Drosophila and yeast genes allows the analysis of the evolution of the GAPDH genes in detail.

/pdf/isolation-and-characterization-of-rat-and-human-454z5flfxe.pdf

Isolation and characterization of rat and human glyceraldehyde-3-phosphate dehydrogenase cDNAs: genomic complexity and molecular evolution of the gene

The rat serum albumin gene has been isolated from a recombinant library containing the entire rat genome cloned in the lambda phage Charon 4A. Preliminary R-loop and restriction analysis has revealed that this gene is split into at least 14 fragments (exons) by 13 intervening sequences (introns), and that it occupies a minimum of 14.5 kilobases of genomic DNA.

https://www.jstor.org/stable/pdfplus/69969.pdf

The rat serum albumin gene: analysis of cloned sequences.

Dlx3 is a homeodomain transcription factor and a member of the vertebrate Distal-less family. Targeted deletion of the mouse Dlx3 gene results in embryonic death between day 9.5 and day 10 because of placental defects that alter the development of the labyrinthine layer. In situ hybridization reveals that the Dlx3 gene is initially expressed in ectoplacental cone cells and chorionic plate, and later in the labyrinthine trophoblast of the chorioallantoic placenta, where major defects are observed in the Dlx3 −/− embryos. The expression of structural genes, such as 4311 and PL-1, which were used as markers to follow the fate of different derivatives of the placenta, was not affected in the Dlx3-null embryos. However, by day 10.5 of development, expression of the paired-like homeodomain gene Esx1 was strongly down-regulated in affected placenta tissue, suggesting that Dlx3 is required for the maintenance of Esx1 expression, normal placental morphogenesis, and embryonic survival.

https://www.pnas.org/content/pnas/96/1/162.full.pdf

Placental failure in mice lacking the homeobox gene Dlx3

DG81 is a cDNA clone derived from a subtracted library containing those RNA molecules that are present in gastrulae but absent from eggs of the frog Xenopus laevis. DG RNAs (where DG indicates differentially expressed in gastrula) represent the products of new transcription activated in the embryo at the midblastula transition or shortly thereafter. DG81 RNA is first detected in middle to late gastrulae, peaks in abundance in early tadpoles, and declines to background levels by the end of metamorphosis. Sequence analysis of an almost full-length cDNA clone homologous to DG81 allows deduction of a protein sequence that shows extensive homology to known intermediate filament proteins, most notably to epidermal type I cytokeratins. Consequently, the protein encoded by DG81 has been named XK81, for Xenopus keratin 81. In concert with keratins analyzed previously, XK81 has a central coiled-coil alpha-helical domain of 312 amino acids, which accounts for most of the homology to other keratins. This rod-like region is flanked by more divergent domains of 73 amino acids at the NH2 terminus and 44 amino acids at the COOH terminus. XK81 provides an example of a cytokeratin whose expression is limited to pre-adult developmental stages. We suggest that XK81 functions specifically in the differentiation of the tadpole epidermis.

Epidermal keratin gene expressed in embryos of Xenopus laevis.

The nucleotide sequences of the recombinant DNA inserts of three bacterial plasmid clones containing nearly all of the rat serum albumin mRNA have been determined. A statistical analysis of the nucleotide sequence reveals a pattern of repeated internal homology that confirms the "intragenic triplication" model of albumin evolution.

https://www.pnas.org/content/pnas/78/1/243.full.pdf

Nucleotide sequence of cloned rat serum albumin messenger RNA

We have determined the sequences of the recombinant DNA inserts of three bacterial plasmid cDNA clones containing most of the rat alpha a-fetoprotein mRNA. The resultant nucleotide sequence of alpha-fetoprotein was exhaustively compared to the nucleotide sequence of the mRNA encoding rat serum albumin. These two mRNAs have extensive homology (50%) throughout and the same intron locations. The amino acid sequence of rat alpha-fetoprotein has been deduced from the nucleotide sequence, and its comparison to rat serum albumin's amino acid sequence reveals a 34% homology. The regularly spaced positions of the cysteines found in serum albumin are conserved in rat alpha-fetoprotein, indicating that these two proteins may have a similar secondary folding structure. These homologies indicate that alpha-fetoprotein and serum albumin were derived by duplication of a common ancestral gene and constitute a gene family.

Thomas D. Sargent

Papers

The rat serum albumin gene: analysis of cloned sequences.

Placental failure in mice lacking the homeobox gene Dlx3

Epidermal keratin gene expressed in embryos of Xenopus laevis.

Nucleotide sequence of cloned rat serum albumin messenger RNA

Sequence homology between RNAs encoding rat alpha-fetoprotein and rat serum albumin.