We describe a cell surface protein that is abundant in liver and has close structural and biochemical similarities to the low density lipoprotein (LDL) receptor. The complete sequence of the protein containing 4544 amino acids is presented. From the sequence a remarkable resemblance to the LDL‐receptor and epidermal growth factor (EGF) precursor is apparent. Three types of repeating sequence motifs entirely account for the extracellular domain of the molecule. These are arranged in a manner resembling four copies of the ligand binding and the EGF‐precursor homologous region of the LDL‐receptor. Following a proline‐rich segment of 17 amino acids are found six consecutive repeats with close homology to EGF. A single membrane‐spanning segment precedes a carboxy‐terminal ‘tail’ of 100 amino acids. This contains two seven‐amino acid sequences with striking homology to the cytoplasmic tail of the LDL‐receptor in the region that contains the signal for clustering into coated pits. The mRNA for this protein is most abundant in liver, brain and lung. By using an antibody raised against a 13‐amino acid peptide corresponding to the deduced amino acid sequence of the carboxy‐terminus of the protein we have demonstrated its existence on the cell surface and its abundance in liver. Like the LDL‐receptor this protein also strongly binds calcium, a cation absolutely required for binding of apolipoproteins B and E to their receptors. We propose that this LDL‐receptor related protein (LRP) is a recycling lipoprotein receptor with possible growth‐modulating effects.

Arrays of up to some 1000 PNA oligomers of individual sequence were synthesised on polymer membranes using a robotic device originally designed for peptide synthesis. At approximately 96%, the stepwise synthesis efficiency was comparable to standard PNA synthesis procedures. Optionally, the individual, fully deprotected PNA oligomers could be removed from the support for further use, because an enzymatically cleavable but otherwise stable linker was used. Since PNA arrays could form powerful tools for hybridisation based DNA screening assays due to some favourable features of the PNA molecules, the hybridisation behaviour of DNA probes to PNA arrays was investigated for a precise understanding of PNA-DNA interactions on solid support. Hybridisation followed the Watson-Crick base pairing rules with higher duplex stabilities than on corresponding DNA oligonucleotide sensors. Both the affinity and specificity of DNA hybridisation to the PNA oligomers depended on the hybridisation conditions more than expected. Successful discrimination between hybridisation to full complementary PNA sequences and truncated or mismatched versions was possible at salt concentrations down to 10 mM Na+and below, although an increasing tendency to unspecific DNA binding and few strong mismatch hybridisation events were observed.

Soluble guanylyl cyclase was purified from bovine lung by an immunoaffinity chromatographic method using IgG fractions of antisera against a synthetic peptide of the C-terminus of the 70-kDa subunit of the enzyme. After anion-exchange chromatography, the enzyme was bound to an immunoaffinity column and was eluted with the synthetic peptide. This method allowed the convenient isolation of 2 mg of apparently homogeneous enzyme from 40 g cytosolic proteins. The enzyme had an apparent molecular mass of about 150 kDa and consisted of two subunits (70 kDa and 73 kDa) as determined by gel permeation fast protein liquid chromatography and SDS/PAGE. The basal activities determined in the presence of Mg2+ and Mn2+ were 10-20 nmol.min-1.mg-1 and 80-100 nmol.min-1.mg-1, respectively. The enzyme exhibited an ultraviolet-visible absorption spectrum typical for hemoproteins, with a Soret band at 430 nm. The purified enzyme was stimulated by NO-containing compounds. Maximal enzyme activities measured in the presence of sodium nitroprusside were 1.2-2.4 mumol.min-1.mg-1 (half-maximal effect of sodium nitroprusside at 1.3-1.9 microM) and 0.9-1.8 mumol.min-1.mg-1 (half-maximal effect at 0.28-0.41 microM sodium nitroprusside) in the presence of Mg2+ and Mn2+, respectively. The method developed for the large-scale purification of soluble guanylyl cyclase by immunoaffinity chromatography, using synthetic peptides for the elution of the enzyme, appears to be superior to previously described methods. As antibodies against synthetic peptides corresponding to deduced amino acid sequences of the respective protein are easily obtained, the described method may be suitable for a convenient large-scale purification of various proteins.

Abstract. Signal recognition particle (SRP) plays the key role in targeting secretory proteins to the membrane of the endoplasmic reticulum (Walter, P., and V. R. Lingappa. 1986. Annu. Rev. CeliBiol. 2:499-516). It consists of SRP7S RNA and six proteins. The 54-kD protein of SRP (SRP54) recognizes the signal sequence of nascent polypeptides. The 19-kD protein of SRP (SRP19) binds to SRP7S RNA directly and is required for the binding of SRP54 to the particle. We used deletion mutants of SRP19 and SRP54 and an in vitro assembly assay in the presence of SRP7S RNA to define the regions in both proteins which are required to form a ribonucleoprotein particle. Deletion of the 21 COOH-terminal amino acids of SRP19 does not interfere with its binding to SRP7S RNA. Further deletions abolish SRP19 binding to SRP7S RNA. The COOH-terminal 207 amino acids of SRP54 (M domain) were found to be necessary and sufficient for binding to the SRP19/7S RNA complex in vitro. Limited protease digestion of purified SRP confirmed our results for SRP54 from the in vitro binding assay. The SRP54M domain could also bind to Escherichia coli 4.5S RNA that is homologous to part of SRP7S RNA. We suggest that the methioninerich COOH terminus of SRP54 is a RNA binding domain and that SRP19 serves to establish a binding site for SRP54 on the SRP7S RNA.

Ribophorins I and II represent proteins that are postulated to be involved in ribosome binding. They are abundant, highly‐conserved glycoproteins located exclusively in the membranes of the rough endoplasmic reticulum. As the first step in the further characterization of the structure and function of these proteins, we have isolated and sequenced full‐length human cDNA clones encoding ribophorins I and II using probes derived from a human liver expression library cloned into pEX1. The authenticity of the clones was verified by overlaps in the protein sequence of N‐terminal and several internal fragments of canine pancreatic ribophorins I and II. The cDNA clones hybridize to mRNA species of 2.5 kb in length, and encode polypeptides of 68.5 and 69.3 kd, respectively. Primary sequence analysis, coupled with biochemical studies on the topology, indicates that both ribophorins are largely luminally disposed, spanning the membrane once and having 150 and 70 amino acid long cytoplasmically disposed C termini, respectively. Both are synthesized as precursors having cleavable signal sequences of 23 (ribophorin I) and 22 (ribophorin II) amino acids. The topology suggested by the primary structure has been confirmed biochemically using proteolytic enzymes and anti‐ribophorin antibodies. Proteolysis of intact microsomes with a variety of enzymes resulted in a reduction in the apparent mol. wt of ribophorin I that would correspond to a loss of its 150‐amino acid cytoplasmic tail. In the case of ribophorin II, it is completely resistant to such proteolysis which is consistent with its luminal disposition and fairly hydrophobic C terminus.(ABSTRACT TRUNCATED AT 250 WORDS)