Conserved amino acid sequences among plant proteins sorted to protein bodies and plant vacuoles. Can they play a role in protein sorting?

A potent neutralizing monoclonal antibody can discriminate amongst IFNgamma from various primates with greater specificity than can the human IFNgamma receptor complex

A monoclonal antibody (AF2) generated against recombinant human interferongamma (IFNgamma) exhibited potent IFNgamma neutralizing activity and prevented human IFNgamma from binding to the cell surface IFNgamma receptor complex. The AF2 antibody also neutralized IFNgamma from higher primates (superfamily Hominoidea) but did not react with IFNgamma from rhesus or other primates in the suborder Anthropoidea IFNgamma from all primates tested, however, could signal via the human IFNgamma receptor complex, as indicated by the ability to upregulate the level of MHC class II molecule expression on the surface of a responsive human cell line. We cloned and sequenced the IFNgamma gene from chimpanzee, gorilla, orangutan, and gibbon, and compared those with the previously reported IFNgamma sequences of human, rhesus, baboon and marmoset. This comparison revealed that, of the primate IFNgammas that were not reactive with AF2, rhesus IFNgamma was most homologous to human IFNgamma, differing at only nine amino acids and containing a one amino acid deletion. Comparing the sequence of human IFNgamma with that of rhesus IFNgamma suggested residues of the human IFNgamma molecule that were involved in the formation of the epitope recognized by the AF2 antibody. Constructing human/rhesus chimeric IFNgamma molecules, combined with site-directed mutagenesis of both human and rhesus IFNgamma revealed that this epitope was dependent upon two non-contiguous amino acids that are juxtaposed in the tertiary structure of IFNgamma. The determinant recognized by AF2 antibody resides in a portion of IFNgamma that is proximal to, but distinct from the surface that interacts with the IFNgamma receptor. Therefore, this neutralizing monoclonal antibody reacts with a conformational determinant that distinguishes primate IFNgammas serologically, but not functionally.

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

Sorting of proteins to vacuoles in plant cells

An individual plant cell may contain at least two functionally and structurally distinct types of vacuoles: protein storage vacuoles and lytic vacuoles. Presumably a cell that stores proteins in vacuoles must maintain these separate compartments to prevent exposure of the storage proteins to an acidified environment with active hydrolytic enzymes where they would be degraded. Thus, the organization of the secretory pathway in plant cells, which includes the vacuoles, has a fascinating complexity not anticipated from the extensive genetic and biochemical studies of the secretory pathway in yeast. Plant cells must generate the membranes to form two separate types of tonoplast, maintain them as separate organelles, and direct soluble proteins from the secretory flow specifically to one or the other via separate vesicular pathways. Individual soluble and membrane proteins must be recognized and sorted into one or the other pathway by distinct, specific mechanisms. Here we review the emerging picture of how separate plant vacuoles are organized structurally and how proteins are recognized and sorted to each type.

A plant metallothionein produced in E. coli

A metallothionein cDNA was generated from pea (Pisum sativum L.) roots, amplified by PCR and inserted into a plasmid for expression in E. coli. Purification of the resultant product generated 3 pools of cadmium-containing material after DEAE-cellulose chromatography. The amino acid composition of each was in excellent agreement with that predicted for pea metallothionein. A cadmium content of approximately 6 g.atoms per mole of protein was estimated. N-terminal sequence analysis revealed that the recombinant molecule had been proteolysed within the extended region linking the 2 cysteine-rich (putative) metal-binding regions. The significance of these findings in terms of the protein folding/targeting of the molecule are considered.