Characterization of pancreatic ERj3p, a homolog of yeast DnaJ-like protein Scj1p

We have previously identified in the human EST sequence data base four overlapping clones that could be aligned with both a predicted protein sequence, deduced from the C. elegans genomic sequence, and partial amino acid sequences, obtained for a protein from canine pancreatic microsomes. We suggested that these proteins are homologs of yeast microsomal and DnaJ-like protein Scj1p and termed them ERj3p. Here we verified the predicted protein sequence of human ERj3p by sequence analysis of the corresponding cDNA. Multiple alignment of related sequences identified these proteins as true homologs of yeast Scj1p. Biochemical analysis of the canine protein characterized ERj3p as a soluble glycoprotein of the pancreatic endoplasmic reticulum. This pancreatic DnaJ-like protein was shown to interact with lumenal DnaK-like proteins, such as BiP. Furthermore, we found that ERj3p interacts with SDF2L1 protein that may be involved in protein O-glycosylation. We propose that ERj3p represents a cochaperone of DnaK-like chaperones of the mammalian endoplasmic reticulum and is involved in folding and maturation of newly synthesized proteins.     

The mechanical hierarchies of fibronectin observed with single-molecule AFM

Mechanically induced conformational changes in proteins such as fibronectin are thought to regulate the assembly of the extracellular matrix and underlie its elasticity and extensibility. Fibronectin contains a region of tandem repeats of up to 15 type III domains that play critical roles in cell binding and self-assembly. Here, we use single-molecule force spectroscopy to examine the mechanical properties of fibronectin (FN) and its individual FNIII domains. We found that fibronectin is highly extensible due to the unfolding of its FNIII domains. We found that the native FNIII region displays strong mechanical unfolding hierarchies requiring 80 pN of force to unfold the weakest domain and 200 pN for the most stable domain. In an effort to determine the identity of the weakest/strongest domain, we engineered polyproteins composed of an individual domain and measured their mechanical stability by single-protein atomic force microscopy (AFM) techniques. In contrast to chemical and thermal measurements of stability, we found that the tenth FNIII domain is mechanically the weakest and that the first and second FNIII domains are the strongest. Moreover, we found that the first FNIII domain can acquire multiple, partially folded conformations, and that their incidence is modulated strongly by its neighbor FNIII domain. The mechanical hierarchies of fibronectin demonstrated here may be important for the activation of fibrillogenesis and matrix assembly.     

SRP-35, a newly identified protein of the skeletal muscle sarcoplasmic reticulum, is a retinol dehydrogenase

In the present study we provide evidence that SRP-35, a protein we identified in rabbit skeletal muscle sarcoplasmic reticulum, is an all-trans-retinol dehydrogenase. Analysis of the primary structure and tryptic digestion revealed that its N-terminus encompasses a short hydrophobic sequence bound to the sarcoplasmic reticulum membrane, whereas its C-terminal catalytic domain faces the myoplasm. SRP-35 is also expressed in liver and adipocytes, where it appears in the post-microsomal supernatant; however, in skeletal muscle, SRP-35 is enriched in the longitudinal sarcoplasmic reticulum. Sequence comparison predicts that SRP-35 is a short-chain dehydrogenase/reductase belonging to the DHRS7C [dehydrogenase/reductase (short-chain dehydrogenase/reductase family) member 7C] subfamily. Retinol is the substrate of SRP-35, since its transient overexpression leads to an increased production of all-trans-retinaldehyde. Transfection of C2C12 myotubes with a fusion protein encoding SRP-35-EYFP (enhanced yellow fluorescent protein) causes a decrease of the maximal Ca2? released via RyR (ryanodine receptor) activation induced by KCl or 4-chloro-m-chresol. The latter result could be mimicked by the addition of retinoic acid to the C2C12 cell tissue culture medium, a treatment which caused a significant reduction of RyR1 expression. We propose that in skeletal muscle SRP-35 is involved in the generation of all-trans-retinaldehyde and may play an important role in the generation of intracellular signals linking Ca2+ release (i.e. muscle activity) to metabolism.     

Effect of antibiotics on ribosomal RNA and proteins from Streptococcus pyogenes

Summary Cells of Streptococcus pyogenes were prepared under rigid conditions. The microorganisms were then incubated for 3 hours in the presence or absence of chloramphenicol, actinomycin or puromycin. RNA, ribosomal fraction and ribosomal proteins were isolated from the cells. The materials were invesigated with the help of infra red spectroscopy using the potassium bromide pellet method. Quantitative differences in the 1750–1500 cm^-1 region were observed with materials treated with the antibiotics. Synthetic mixtures of ribosomal RNA with progressively larger amounts of ribosomal proteins show analogous changes, namely a progressive increase in the strength of the 1650 cm^-1 band relative to the 1685 cm^-1 band, and an increase in the 1535 cm^-1 band. The analytical results obtained with the ribosomal RNA isolated from S. pyogenes treated with antibiotics indicated increased amounts of proteins which could not be removed by the applied extraction method. The evidence presented suggests a change in the binding between ribosomal RNA and ribosomal proteins in the material isolated from the antibiotic treated microorganisms. The I. R. spectroscopy seems to be an useful tool in the investigation of some aspects of biological materials.     

N-Acetyl-l-cysteine abolishes the bromoethylamine-induced choline incorporation into renal papillary tissue

The role of regenerative processes in the protective effect of N-acetyl-L-cysteine (NAC) against bromoethylamine-induced renal papillary necrosis was assessed in rats given bromoethylamine (BEA) (1.2 mmol/kg), N-acetylcysteine (6 mmol/kg), or N-acetylcysteine plus BEA. Renal papillary slices were dissected after 15 hours of treatment, and ¹⁴C-choline incorporation into total phospholipid, lysophosphatidylcholine, sphingomyelin, and phosphatidylcholine was measured. Bromoethylamine elicited an increase in the incorporation of ¹⁴C-choline into choline-containing phospholipid, an effect that was abolished when N-acetylcysteine was administered prior to bromoethylamine. These studies indicate that the defensive mechanism of N-acetylcysteine against bromoethylamine-induced renal papillary necrosis is not related to regenerative processes and that N-acetylcysteine abolishes the bromoethylamine-induced choline incorporation into papillary phospholipid. © 1996 John Wiley & Sons, Inc.