A multimeric protein that behaves functionally as an authentic ferritin has been isolated from the Gram-positive bacterium Listeria innocua. The purified protein has a molecular mass of about 240,000 Da and is composed of a single type of subunit (18,000 Da). L. innocua ferritin is able to oxidize and sequester about 500 iron atoms inside the protein cage. The primary structure reveals a high similarity to the DNA-binding proteins designated Dps. Among the proven ferritins, the most similar sequences are those of mammalian L chains that appear to share with L. innocua ferritin the negatively charged amino acids corresponding to the iron nucleation site. In L. innocua ferritin, an additional aspartyl residue may provide a strong complexing capacity that renders the iron oxidation and incorporation processes extremely efficient. This study provides the first experimental evidence for the existence of a non-heme bacterial ferritin that is related to Dps proteins, a finding that lends support to the recent suggestion of a common evolutionary origin of these two protein families.

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Dystroglycan (DG) is an adhesion molecule playing a crucial role for tissue stability during both early embriogenesis and adulthood and is composed by two tightly interacting subunits: R-DG, membrane-associated and highly glycosylated, and the transmembrane -DG. Recently, by solid-phase binding assays and NMR experiments, we have shown that the C-terminal domain of R-DG interacts with a recombinant extracellular fragment of -DG (positions 654-750) independently from glycosylation and that the linear binding epitope is located between residues 550 and 565 of R-DG. In order to elucidate which moieties of -DG are specifically involved in the complex with R-DG, the ectodomain has been recombinantly expressed and purified in a labeled ( 13 C, 15 N) form and studied by multidimensional NMR. Although it represents a natively unfolded protein domain, we obtained an almost complete backbone assignment. Chemical shift index, 1 H-15 N heteronuclear single-quantum coherence and nuclear Overhauser effect (HSQC-NOESY) spectra and 3 J HN,HR coupling constant values confirm that this protein is highly disordered, but 1 H-15 N steady-state NOE experiments indicate that the protein presents two regions of different mobility. The first one, between residues 659 and 722, is characterized by a limited degree of mobility, whereas the C-terminal portion, containing about 30 amino acids, is highly flexible. The binding of -DG(654-750) to the C-terminal region of the R subunit, R-DG(485-620), has been investigated, showing that the region of -DG(654-750) between residues 691 and 719 is involved in the interaction. † The financial support of CNR, target project "Biotechnology" and

The dystroglycan (DG) adhesion complex is formed by the peripheral α-DG and the transmembrane β-DG, both originating from the same precursor. α-DG plays a crucial role for tissue stability since it binds with high affinity a variety of proteins and proteoglycans in many different cell types. One common molecular feature of most of the α-DG ligands is the presence of laminin globular (LG) domains that are likely to interact with some of the carbohydrates protruding from the mucin-like region of α-DG. Every tissue is supposed to produce a specific α-DG harboring a particular sugar moiety that will enable it to bind a specific ligand, but often several α-DG ligands are co-expressed within the same tissue. It is therefore very important to assess all these different interactions, ultimately measuring the affinity constants (KDs) underlying them. Herein, we present an updated list of α-DG interactors, including non LG-domains containing ligands, offering both a historic perspective on the original contributions made by several laboratories and an update on the different techniques used and the KD values obtained so far. For the cure of some muscular dystrophies, the reinstatement of a prominent affinity between α-DG and one of its vicarious ligands is becoming an increasingly popular choice for strengthening the basement membrane-tissue connection. An update on the current available information about α- DG's multiple, and often "concomitant" affinities, may be of interest for those wishing to better direct their molecular therapy approaches. A final paragraph is dedicated to comment on the evidence that an increase in affinity is not always advantageous.