PubMed Health⌕ Search

Biomedical subjects

R S Jamison

Publications and source records attributed to R S Jamison.

8 recordsLinked to original sources
PubMed1995

Test of the contribution of an amino-aromatic hydrogen bond to protein function.

Hydrogen bonds which form between a hydrogen bond donor and an aromatic ring as acceptor are thought to contribute to the stability and function of proteins. We have tested the function of such an interaction in a highly homologous pair of proteins, cellular retinol-binding protein (CRBP) and cellular retinol-binding protein, type II [CRBP(II)]. Both proteins bind the ligand all-trans-retinal with comparable affinities, but CRBP has an approximately 100-fold higher affinity for all-trans retinal. The greater affinity of CRBP for all-trans-retinol has been attributed to the presence of an amino-aromatic hydrogen bond, which is absent in CRBP(II). We have generated a pair of mutant proteins, in which the amino-aromatic interaction was removed from CRBP and introduced into CRBP(II). Spectral analyses of retinol when bound to the wild-type and mutant CRBP suggested that it adopted an identical conformation within both proteins, a conformation that was distinct from that of retinol bound to CRBP(II), both wild-type and mutant. Unexpectedly, the affinities of the mutant binding proteins for all-trans-retinol were indistinguishable from those of their corresponding wild-type proteins. Further, in ligand competition experiments, there were no observable differences between mutant and wild-type CRBP, or between mutant and wild-type CRBP(II), in their preferences for binding all-trans-retinol versus all-trans-retinal. The results of this direct test of the proposed function of an amino-aromatic hydrogen bond did not support a functional role for such bonds, at least in this system.

Animals↗
PubMed1994

Cellular retinoid-binding proteins: limited proteolysis reveals a conformational change upon ligand binding.

Intracellular retinoid-binding proteins are small, tightly folded, compact proteins, which appear to be involved in the delivery of retinoids to microsomal metabolic enzymes, among other potential roles. Recently, it has been demonstrated that two of these binding proteins, cellular retinol-binding protein (CRBP) and cellular retinol-binding protein type II [CRBP(II)], interact with the same microsomal enzyme but in different manners, depending on the absence or presence of ligand [Herr, F.M., & Ong, D.E. (1992) Biochemistry 31, 6748-6755]. The structural components of the binding proteins responsible for these differential interactions are presently unknown. In addition, it is not clear how the ligand is able to gain entry into the solvent-inaccessible interior binding cavity. Limited proteolysis of the apo and holo forms of CRBP and CRBP(II) was used to probe the conformational differences between the different states of these two proteins in solution. It was found that the apo forms of both proteins were significantly more susceptible to proteolysis, and probably adopted a more open conformation, than the holo forms. The initial cleavage site of endoproteinase Arg-C in the apo forms occurred at a conserved arginine residue near a possible site of ligand entry. Similar results were obtained by limited proteolysis of cellular retinoic acid-binding protein and heart fatty acid-binding protein, indicating that a common ligand-induced conformational change may occur for other members of this family of intracellular binding proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

A novel, testis-specific member of the cellular lipophilic transport protein superfamily, deduced from a complimentary deoxyribonucleic acid clone.

A novel member of the cellular lipophilic transport protein superfamily was identified after an antiserum raised against cellular retinoic acid-binding protein (CRABP) was found also to contain antibodies against another 15-kDa protein present in the cytosol of pubertal and adult rat testis. These antibodies were used to screen a rat testis cDNA expression library and isolate a 561-bp clone containing a full open reading frame from which the sequence of a novel 132 amino acid protein was deduced. The protein has 58% amino acid sequence identity to bovine myelin P2, 58% identity to murine adipocyte lipid-binding protein, and 40% identity to rat CRABP. Although the endogenous ligand has not yet been identified, conservation of residues involved in the binding of carboxylate groups suggests that the ligand is a fatty acid or an acidic retinoid. Tissue-specific expression was examined by Northern analysis and immunolocalization and appears to be restricted to late germ cells within the testis and epididymis. Immunostaining was first detectable in mid-pachytene spermatocytes and increased in intensity as these cells progressed to elongated spermatids, suggesting that this testis lipid-binding protein has a specific role in sperm development.

Amino Acid Sequence↗
PubMed1993

The evolutionary history of the first three enzymes in pyrimidine biosynthesis.

Some metabolic pathways are nearly ubiquitous among organisms: the genes encoding the enzymes for such pathways must therefore be ancient and essential. De novo pyrimidine biosynthesis is an example of one such metabolic pathway. In animals a single protein called CAD carries the first three steps of this pathway. The same three enzymes in prokaryotes are associated with separate proteins. The CAD gene appears to have evolved through a process of gene duplication and DNA rearrangement, leading to an in-frame gene fusion encoding a chimeric protein. A driving force for the creation of eukaryotic genes encoding multienzymatic proteins such as CAD may be the advantage of coordinate expression of enzymes catalyzing steps in a biosynthetic pathway. The analogous structure in bacteria is the operon. Differences in the translational mechanisms of eukaryotes and prokaryotes may have dictated the different strategies used by organisms to evolve coordinately regulated genes.

Animals↗
PubMed1992

Complete hamster CAD protein and the carbamylphosphate synthetase domain of CAD complement mammalian cell mutants defective in de novo pyrimidine biosynthesis.

The mammalian CAD gene codes for a 240-kDa multifunctional protein that catalyzes the first three steps of de novo pyrimidine biosynthesis. Previously, the longest cDNA construct available was missing approximately 500 bp of coding sequence at the 5' end, thereby lacking the sequence to encode the entire carbamylphosphate synthetase (CPSase) domain. Here, a complete CAD hamster cDNA is constructed, placed into a mammalian expression vector, and transfected into hamster cells deficient in CAD. Transfectants show coordinately restored levels of all three enzyme activities and the presence of full-length CAD protein. A derivative construct of the CAD cDNA was generated that should encode only the CPSase domain. When transfected into mammalian cells, a protein was synthesized that had significant CPSase activity both in vivo and in vitro. The two constructs generated in this study will facilitate the study of CAD structure, function, and allosteric regulation.

Amino Acid Sequence↗