The two forms of chicken cystatin, with different isoelectric points, that have been described previously were indistinguishable in analyses of amino- and carboxy-terminal residues, amino acid composition, and peptide maps. The two forms thus are highly similar and most likely differ only in an amide group or in a small charged substituent. The binding of either cystatin form to highly purified, active papain was accompanied by the same pronounced changes in near-ultraviolet circular dichroism, ultraviolet absorption, and fluorescence emission. These changes were compatible with perturbations of the environment of aromatic residues in one or both proteins of the complex, arising from local interactions or from a conformational change. Modification of the single tryptophan residue of cystatin, at position 104, with N-bromosuccinimide resulted in considerably smaller spectroscopic changes on binding of the inhibitor to papain, indicating that the environment of this residue is affected by the binding. Analogous modification of Trp-69 and Trp-177 of papain markedly affected the fluorescence changes observed on binding of cystatin to the enzyme, similarly suggesting that these two residues of papain are involved in the interaction. The fluorescence increase of papain at alkaline pH, arising from Trp-177 and due to deprotonization of the adjacent His-159, was abolished on binding of cystatin to the enzyme, further supporting the proposal that this region of papain participates in the interaction with the inhibitor. A stoichiometry of binding of either cystatin form to papain of 1:1 and a lower limit for the binding constant of 10(9) M-1 were determined by titrations monitored by either the ultraviolet absorption or fluorescence changes induced by the interaction.

The gene encoding the IgG‐binding protein G from Streptococcus G148 was isolated by molecular cloning. A subclone containing a 1.5‐kb insert gave a functional product in Escherichia coli. Protein analysis of affinity‐purified polypeptides revealed two gene products, both smaller than protein G spontaneously released from streptococci, but with identical IgG‐binding properties. The complete nucleotide sequence of the insert revealed a repeated structure probably evolved through duplications of fragments of different sizes. The deduced amino acid sequence revealed an open reading frame extending throughout the insert, terminating in a TAA stop codon. Analysis of the two gene products by N‐terminal amino acid determination suggests that two different TTG codons are recognized in E. coli for initiation of translation to yield the two products. Based on these results several truncated gene constructions were expressed and analysed. The results suggest that the C‐terminal part of streptococcal protein G consists of three IgG‐binding domains followed by a region which anchors the protein to the cell surface. Structural and functional comparisons with streptococcal M protein and staphylococcal protein A have been made.

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p53 triggers cell cycle arrest and apoptosis through transcriptional regulation of specific target genes. We have investigated the effect of p53 activation on the proteome using 2D gel electrophoresis analysis of mitomycin C-treated HCT116 colon carcinoma cells carrying wild-type p53. Approximately 5,800 protein spots were separated in overlapping narrow-pH-range gel strips, and 115 protein spots showed significant expression changes upon p53 activation. The identity of 55 protein spots was obtained by mass spectrometry. The majority of the identified proteins have no previous connection to p53. The proteins fall into different functional categories, such as mRNA processing, translation, redox regulation, and apoptosis, consistent with the idea that p53 regulates multiple cellular pathways. p53-dependent regulation of five of the up-regulated proteins, eIF5A, hnRNP C1/C2, hnRNP K, lamin A/C, and Nm23-H1, and two of the down-regulated proteins, Prx II and TrpRS, was examined in further detail. Analysis of mRNA expression levels demonstrated both transcription-dependent and transcription-independent regulation among the identified targets. Thus, this study reveals protein targets of p53 and highlights the role of transcription-independent effects for the p53-induced biological response.proteomics ͉ transcription factor ͉ cancer

A fetal form of somatomedin (insulin-like growth factor) that crossreacts in the fetal brain radioreceptor assay has been proposed to exist in humans. Using this assay to monitor activity during purification, we have isolated a variant form of insulin-like growth factor I (IGF-I) from human fetal brain tissue. The variant IGF-I showed potent crossreaction in the fetal brain radioreceptor assay and stimulated DNA synthesis in fetal brain cells in vitro. Structural analysis revealed the variant IGF-I to have a truncated NH2-terminal region compared to IGF-I isolated from serum. An additional peptide, which displayed less potent crossreaction in the fetal brain radioreceptor assay, was also isolated from the human fetal brain. Partial amino acid sequence analysis revealed identity to insulin-like growth factor II.