Over the last decade, the concept of an IGFBP family has been well accepted, based on structural similarities and on functional abilities to bind IGFs with high affinities. The existence of other potential IGFBPs was left open. The discovery of proteins with N-terminal domains bearing striking structural similarities to the N terminus of the IGFBPs, and with reduced, but demonstrable, affinity for IGFs, raised the question of whether these proteins were "new" IGFBPs (22, 23, 217). The N-terminal domain had been uniquely associated with the IGFBPs and has long been considered to be critical for IGF binding. No other function has been confirmed for this domain to date. Thus, the presence of this important IGFBP domain in the N terminus of other proteins must be considered significant. Although these other proteins appear capable of binding IGF, their relatively low affinity and the fact that their major biological actions are likely to not directly involve the IGF peptides suggest that they probably should not be classified within the IGFBP family as provisionally proposed (22, 23). The conservation of this single domain, so critical to high-affinity binding of IGF by the six IGFBPs, in all of the IGFBP-rPs, as well, speaks to its biological importance. Historically, and perhaps, functionally, this has led to the designation of an "IGFBP superfamily". The classification and nomenclature for the IGFBP superfamily, are, of course, arbitrary; what is ultimately relevant is the underlying biology, much of which still remains to be deciphered. The nomenclature for the IGFBP related proteins was derived from a consensus of researchers working in the IGFBP field (52). Obviously, a more general consensus on nomenclature, involving all groups working on each IGFBP-rP, has yet to be reached. Further understanding of the biological functions of each protein should help resolve the nomenclature dilemma. For the present, redesignating these proteins IGFBP-rPs simplifies the multiple names already associated with each IGFBP related protein, and reinforces the concept of a relationship with the IGFBPs. Beyond the N-terminal domain, there is a lack of structural similarity between the IGFBP-rPs and IGFBPs. The C-terminal domains do share similarities to other internal domains found in numerous other proteins. For example, the similarity of the IGFBP C terminus to the thyroglobulin type-I domain shows that the IGFBPs are also structurally related to numerous other proteins carrying the same domain (87). Interestingly, the functions of the different C-terminal domains in members of the IGFBP superfamily include interactions with the cell surface or ECM, suggesting that, even if they share little sequence similarities, the C-terminal domains may be functionally related. The evolutionary conservation of the N-terminal domain and functional studies support the notion that IGFBPs and IGFBP-rPs together form an IGFBP superfamily. A superfamily delineates between closely related (classified as a family) and distantly related proteins. The IGFBP superfamily is therefore composed of distantly related families. The modular nature of the constituents of the IGFBP superfamily, particularly their preservation of an highly conserved N-terminal domain, seems best explained by the process of exon shuffling of an ancestral gene encoding this domain. Over the course of evolution, some members evolved into high-affinity IGF binders and others into low-affinity IGF binders, thereby conferring on the IGFBP superfamily the ability to influence cell growth by both IGF-dependent and IGF-independent means (Fig. 10). A final word, from Stephen Jay Gould (218): "But classifications are not passive ordering devices in a world objectively divided into obvious categories. Taxonomies are human decisions imposed upon nature--theories about the causes of nature's order. The chronicle of historical changes in classification provides our finest insight into conceptual revolutions

/pdf/the-insulin-like-growth-factor-binding-protein-igfbp-41vwms7yip.pdf

The insulin-like growth factor-binding protein (IGFBP) superfamily.

Handbook of LEGUMES of World Economic Importance

Plant cell walls are amazingly complex amalgams of carbohy? drates, proteins, lignin, water, and incrusting substances such as cutin, suberin, and certain inorganic compounds that vary among plant species, cell types, and even neighboring cells Developmental events and exposure to any of a number of abiotic and biotic stresses further increase this compositional and structural variation Moreover, the dynamic nature and func? tions of plant cell walls in terms of growth and development, environmental sensing and signaling, plant defense, intercel? lular communication, and selective exchange interfaces are reflected in these variations Much is currently known about the structure and metabolic regulation of the various cell wall components, but relatively little is known about their precise functions and intermolecular interactions In this review, I will discuss the accumulated structural and regulatory data and the much more limited functional and in? termolecular interaction information on five plant cell wall protein classes These five protein classes, listed in Table 1, include the extensins, the glycine-rich proteins (GRPs), the proline-rich proteins (PRPs), the solanaceous lectins, and the arabinogalactan proteins (AGPs) These five proteins may be evolutionarily related to one another, most obviously because each of them, with the exception of the GRPs, contains hydroxyproline, and less obviously in the case of the GRPs because this class has nucleotide sequence similarity to the extensins For completeness, I should mention that these are not the only cell wall proteins that are known Others exist, such as cysteine-rich thionins, 28and 70-kD water-regulated proteins, a histidine-tryptophan-rich protein, and many cell wall enzymes such as peroxidases, phosphatases, invertases, a-mannosidases, P-mannosidases, p-1,3-glucanases, (3-1,4glucanases, polygalacturonase, pectin methylesterases, malate dehydrogenase, arabinosidases, a-galactosidases, (3-galactosidases, |3-glucuronosidases, p-xylosidases, proteases, and ascorbic acid oxidase (Varner and Lin, 1989) However, the above five classes generally represent the most abundant, and to date, the most well-studied and widely documented, plant cell wall proteins Before describing these five wall protein classes, I should point out that research on these individual proteins has oc? curred in several plant species, but relatively few examples exist where these cell wall proteins have been studied together in one plant, let alone in one particular plant organ or type of cell Thus, data from one plant species are often extrapolated to represent the situation in other plant species Although such extrapolations are usually valid, enough variations are now known that caution should be exercised in making or believing such claims

Structure and function of plant cell wall proteins.

Legumin and vicilin, storage proteins of legume seeds

Plants produce a range of ligands for cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn). Cd- and Zn-citrate complexes are prevalent in leaves, even though malate is more abundant. In the xylem sap moving from roots to leaves, citrate and histidine are the principal ligands for Cu, Ni, and Zn. Phosphorus-rich globular bodies in young roots are probably Zn-phytate. Metallothioneins (MTs) are cysteine (Cys)-rich ligands. Plants produce class II MTs (MT-IIs) which differ from the archetypal mammalian MT-I in the location and number of Cys. The Ec protein from wheat embryos has Cys in three domains, binds Zn, and disappears with seedling development. The first 59 amino acids have been sequenced for the protein. Fifty-eight genes for MT-IIs, from a range of plants and tissues, predict proteins with Cys in two domains. Most of the predicted proteins have not been isolated, and their metal binding is poorly documented. Three protein bands, corresponding to six MT genes, have been isolated fromArabidopsis, and the amino acids sequenced for nine fragments. The MT-IIIs are atypical, nontranslationally synthesized polypeptides with variously repeating γ-glutamylcysteine units. Of the five families known, those with carboxy-terminal glycine are the most widespread among plants, algae, and certain yeasts. A heterogeneous grouping of these molecules form Cd-binding complexes with tetrahedral coordination and a Cd-sulfur interatomic distance of 2.52 A. One complex is cytosolic, the dominant one is vacuolar. Together, they can bind a large proportion of cellular Cd; other ligands may also function. Little is known about the counterpart situation for Cu and Zn.

Structure and function of metal chelators produced by plants: the case for organic acids, amino acids, phytin, and metallothioneins.

The POLARIS (PLS) gene of Arabidopsis was identified as a promoter trap transgenic line, showing beta-glucuronidase fusion gene expression predominantly in the embryonic and seedling root, with low expression in aerial parts. Cloning of the PLS locus revealed that the promoter trap T-DNA had inserted into a short open reading frame (ORF). Rapid amplification of cDNA ends PCR, RNA gel blot analysis, and RNase protection assays showed that the PLS ORF is located within a short ( approximately 500 nucleotides) auxin-inducible transcript and encodes a predicted polypeptide of 36 amino acid residues. pls mutants exhibit a short-root phenotype and reduced vascularization of leaves. pls roots are hyperresponsive to exogenous cytokinins and show increased expression of the cytokinin-inducible gene ARR5/IBC6 compared with the wild type. pls seedlings also are less responsive to the growth-inhibitory effects of exogenous auxin and show reduced expression of the auxin-inducible gene IAA1 compared with the wild type. The PLS peptide-encoding region of the cDNA partially complements the pls mutation and requires the PLS ORF ATG for activity, demonstrating the functionality of the peptide-encoding ORF. Ectopic expression of the PLS ORF reduces root growth inhibition by exogenous cytokinins and increases leaf vascularization. We propose that PLS is required for correct auxin-cytokinin homeostasis to modulate root growth and leaf vascular patterning.

The POLARIS Gene of Arabidopsis Encodes a Predicted Peptide Required for Correct Root Growth and Leaf Vascular Patterning

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2890%2980145-9

A gene from pea (Pisum sativum L.) with homology to metallothionein genes

Polypeptide material has been immunoprecipitated by antivicilin antibodies from translation products of polyribosomes and poly(A)-rich RNA isolated from developing seeds of Pisum sativum in the wheat germ and reticulocyte lysate cell-free synthesis systems. Analysis of this material by SDS-PAGE shows it to consist of three bands, of molecular weights 70,000, 50,000 and 47,000. The in vitro vicilin polypeptides of 70,000 and 50,000 mol. wt. have been shown to be very similar to the 70,000 and 50,000 mol. wt. subunits of vicilin by specific immunoprecipitation, and behaviour on treatment with cyanogen bromide and trypsin. The 50,000 mol. wt. in vitro vicilin polypeptide contains no significant extra sequence compared to the 50,000 mol. wt. vicilin subunit. The 47,000 mol. wt. in vitro vicilin polypeptide has no corresponding subunit in vicilin from mature seeds, but a 47,000 mol. wt. subunit is present in vicilin isolated from developing seeds. Comparison of translation products from polysomes isolated from seeds at middle and late stages of development shows that synthesis of the 50,000 and 47,000 mol. wt., but not 70,000 mol. wt. polypeptides is very much reduced at late stages of development. These results are discussed with reference to the nature of the vicilin fraction.

Characterisation of the storage protein subunits synthesised in vitro by polyribosomes and RNA from developing pea (Pisum sativum L.) : II. Vicilin.

Polyribosomes which have template activity in the wheat germ system have been isolated from developing pea seeds. Some of the translation products have identical mobilities to the vicilin and legumin subunits by SDS-PAGE. Certain products were specifically immunoprecipitated with antisera prepared against purified vicilin and legumin fractions. Various RNA fractions including poly A-rich RNA have also been isolated from polyribosomes and shown to direct the synthesis of polyripeptides whose properties are similar to the storage protein subunits. The results are discussed in relationship to other investigations with seed storage protein biosynthesis in vitro.

Cell free synthesis of some storage protein subunits by polyribosomes and RNA isolated from developing seeds of pea ( Pisum sativum L.)

A pea genomic library was screened with a pea seed lectin cDNA clone, a selected clone sub-cloned and the DNA sequence determined. We have designated this gene LecA; like other lectin genes LecA contains no introns. The coding sequence of this gene is identical to that of the cDNA used to select it, pLGA.10 (1) and that of the published cDNA sequence (2). Although these cDNAa differ in their sites of polyadenylation there is only one (simple) polyadenylation signal. At the 5' end of the gene there are three in frame ATG start codons. The first of these is followed by an in frame stop codon and both the sequence surrounding thio and the third ATG are poor matches to the functional consensus (3). The second agrees well and is therefore used. Multiple start codons have been noted in lectin genes from Phaseolus vulgaris (4). LecA contains a TATA box (5) 65 bases 5' to the start codon which lies within a 22bp region duplicated between this and the start codon; such repeats also occur in Phaseolus lectin genes (4). No other consensus seqquences can be recognised in the further 5' flanking sequence and comparison with lectin genes from related species (4, 6, 7) failed to reveal regions of significant homology. When this gene was used to probe Southern blots of restriction digests of pea genomic DNA at high stringency of hybridisation, to determine the copy number of LecA, all digests gave a result indicating the presence of a single gene.

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I. Marta Evans

Papers

The POLARIS Gene of Arabidopsis Encodes a Predicted Peptide Required for Correct Root Growth and Leaf Vascular Patterning

A gene from pea (Pisum sativum L.) with homology to metallothionein genes

Characterisation of the storage protein subunits synthesised in vitro by polyribosomes and RNA from developing pea (Pisum sativum L.) : II. Vicilin.

Cell free synthesis of some storage protein subunits by polyribosomes and RNA isolated from developing seeds of pea ( Pisum sativum L.)

Sequence of the seed lectin gene from pea (Pisum sativum L.).