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PubMed1990

Membranes.

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Animals↗
PubMed1991

The protein translocation apparatus of the rough endoplasmic reticulum, its associated proteins, and the mechanism of translocation.

The demonstration that the yeast Sec61, Sec62, and Sec63 proteins are assembled into a multisubunit complex in the yeast endoplasmic reticulum was of particular significance in a year when protein, and nucleic-sequence analyses revealed interesting homologies between pathways of protein transport in mammals and yeast, and possibly in Escherichia coli.

Animals↗
PubMed1992

Protein sorting in mitochondria.

Most polypeptides that are imported into the mitochondrial matrix use a common translocation machinery. By contrast, proteins of the other mitochondrial compartments are imported by a variety of different mechanisms. Some of these proteins completely bypass the common translocation machinery, others use only the outer membrane components of this machinery, and still others use components of this machinery from both the outer and inner membranes. Import to the intermembrane space compartment provides examples of all three possibilities.

Amino Acid Sequence↗
PubMed1988

Identification of a polypeptide secreted by human breast cancer cells (MCF-7) as the human estrogen-responsive gene (pS2) product.

Human epidermal growth factor-like immunoreactive factor (designated as EGF-LI) synthesized and secreted by human breast cancer cells, strain MCF-7, was isolated in pure form. Thirty-seven micrograms of EGF-LI was purified by anion-exchange, gel permeation, and reverse-phase high-performance liquid chromatography from 2 liters of serum-free medium conditioned by the cells. The sequence of the first 36 amino acids from the N-terminus was determined with a gas-phase protein sequencer. Computer-assisted screening revealed, quite unexpectedly, this sequence to be completely identical to that of the translational product encoded by pS2, the human estrogen-responsive gene, over the region extending from residue 25 to 60 (Jakowlew, S. B. et al. (1984) Nucleic Acids Res., 12, 2861-2878).

Amino Acid Sequence↗
PubMed1992

Identification of functional arginines in human angiogenin by site-directed mutagenesis.

Chemical modifications of human angiogenin had suggested that arginines are essential for its ribonucleolytic activity [Shapiro, R., Weremowicz, S., Riordan, J. F., & Vallee, B. L. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 8783-8787]. Each of the six arginines within or near angiogenin's catalytic or cell-binding sites--i.e., those at positions 5, 31, 32, 33, 66, and 70--was therefore mutated to alanine. Two of these residues, Arg-5 and Arg-33, indeed play a role, albeit noncrucial, in enzymatic activity, although neither one is implicated in the abolition of activity by arginine reagents. R5A-angiogenin, while nearly fully active toward dinucleotides, is one-fourth as active as angiogenin toward tRNA, suggesting that Arg-5 may participate in the binding of peripheral components of the substrate. In contrast, the activity of R33A-angiogenin toward both polynucleotide and dinucleotide substrates is reduced similarly, reflecting a decrease in kcat. These results, together with its position in the calculated three-dimensional structure of angiogenin, imply an indirect role for Arg-33 in catalysis. Three arginines are important for angiogenesis: mutation of Arg-5, Arg-33, or Arg-66 dramatically reduces the angiogenic potency of angiogenin on the chicken embryo chorioallantoic membrane. Arg-66 lies within a segment previously proposed to be part of a cell-surface receptor binding site. Arg-5 and Arg-33 are outside of this site as defined at present, and the decreased angiogenicity of R5A- and R33A-angiogenin may be a consequence of their reduced ribonucleolytic activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine↗
PubMed1991

Complex pattern of alternative splicing generates unusual diversity in the leader sequence of the chicken link protein mRNA.

We report here the isolation of the 5' end and the promoter region of the gene for chicken cartilage link protein, and demonstrate extensive heterogeneity of the leader sequence arising from differential utilization of multiple splice sites within the 5'-most exon. The 500-base pairs (bp) exon 1 consists of solely untranslated sequence and is followed by an intron greater than 33 kilobase pairs (kb). Together, the five exons predict a gene size longer than 100 kb. Multiple transcription initiation sites were mapped 34, 46, 56, 66 and 76 bp downstream of a TATA-like motif. Sequence analysis revealed that in addition to the non-spliced variant, multiple mRNA species were generated by alternative splicing resulting in the exclusion of 92, 166, 170, 174 and 263 nucleotides (nt), respectively, from exon 1. Polymerase chain reaction confirmed the existence of various splice forms, and showed cell type- and developmental stage-specific expression for one group of them. Secondary structure predictions indicated that the leaders of the splice forms could form stable hairpin structures with different free energies of formation (up to delta G = -110 kcal/mol), suggesting translational control. The splice variant detected in the largest amount had the least stable predicted hairpin (delta G = -31.7 kcal/mol).

Animals↗
PubMed1992

Identification of the disulfide bonds in human plasma protein SP-40,40 (apolipoprotein-J).

SP-40,40, a human plasma protein, is a modulator of the membrane attack complex formation of the complement system as well as a subcomponent of high-density lipoproteins. In the present study, the positions of the disulfide bonds in SP-40,40 were determined. SP-40,40 was purified from human seminal plasma by affinity chromatography using an anti-SP-40,40 monoclonal antibody and reversed-phase, high-performance liquid chromatography (HPLC). The protein was digested with trypsin and the fragments were separated by reversed-phase HPLC. The peptides containing disulfide bonds were fluorophotometrically detected with 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (ABD-F). The peptides containing more than two disulfide bonds were further digested with Staphylococcus aureus V8 protease and lysylendopeptidase, and the fragments were isolated by HPLC. The amino acid compositions and the amino acid sequences of the peptides containing only a disulfide bond were determined. Disulfide bonds thus determined were between Cys58(alpha)-Cys107(beta), Cys68(alpha)-Cys99(beta), Cys75(alpha)-Cys94(beta), and Cys86(alpha)-Cys80(beta). Since there was no free sulfhydryl groups in the SP-40,40 molecule, Cys78(alpha) and Cys91(beta) should also be linked by a disulfide bond. It is notable that all of the disulfide bonds in SP-40,40 are not only formed by inter-chain pairing, but also appear to form an antiparallel ladder-like structure between the two chains. The unique structure could be related to the functions of SP-40,40.

Amino Acid Sequence↗
PubMed1989

Unity in function in the absence of consensus in sequence: role of leader peptides in export.

Passage of proteins across membranes during export from their site of synthesis to their final destination is mediated by leader peptides that paradoxically exhibit a unity of function in spite of a diversity of sequence. These leader peptides act in at least two stages of the export process: at entry into the pathway and subsequently during translocation across the membrane. How selectivity is imposed on the system in the absence of a consensus among the sequences of leader peptides is the main issue discussed here.

Amino Acid Sequence↗