The oncoprotein E7 of human papilloma viruses (HPV) is involved in the pathogenesis and maintenance of human cervical cancers. The most prevalent HPV types found in cervix carcinomas are HPV16, 18 and 45. The structure of the E7 dimer from HPV45 (PDB 2F8B) was determined by nuclear magnetic resonance spectroscopy. Each monomer comprises an unfolded N-terminus and a well-structured C-terminal domain with a b1b2a1b3a2 topology representing a unique zinc-binding fold found only for E7. Dimerization occurs through the a1/a1 0 helices and intermolecular b-sheet formation but excludes the zinc-binding sites. E7 is reported to interact with a number of cellular proteins (e.g. pRb, p21 CIP1 ). Binding of a peptide derived from the C-terminus of p21CIP1 to the Cterminal domain of E7 was characterized by monitoring chemical shift perturbations of the amide groups of E7. This provides direct evidence that a shallow groove situated between a1 and b1 of the E7 C-terminal domain is interacting with the C-terminus of p21 CIP1. Intriguingly, this binding site overlaps with the low-affinity binding site on E7 for the C-domain of pRb.

Regulatory heme binds to specific motifs in proteins and controls a variety of biochemical processes. Several of these proteins were recently shown to form complexes with ferric and/or ferrous heme via a cysteine residue as axial ligand. The objective of this study was to examine the heme-binding properties of a series of cysteine-containing peptides with focus on CP motif sequences. The peptides displayed different binding behavior upon Fe(III) heme application with characteristic wavelength shifts of the Soret band to 370 nm or 420-430 nm and in some cases to both wavelengths. Whereas for most of the peptides containing a cysteine only a shift to 420-430 nm was observed, CP-containing peptides exhibited a preference for a shift to 370 nm. Detailed structural investigation using Raman and NMR spectroscopy on selected representatives revealed different binding modes with respect to iron ion coordination, which reflected the results of the UV-vis studies. A predicted short sequence stretch derived from dipeptidyl peptidase 8 was additionally examined with respect to CP motif binding to heme on the peptide as well as on the protein level. The heme association was confirmed with the first solution structure of a CP-peptide-heme complex and, moreover, an inhibitory effect of Fe(III) heme on the enzyme's activity. The relevance of both the use of model compounds to elucidate the molecular mechanism underlying regulatory heme binding and its potential for the investigation of regulatory heme control is discussed.

To ensure appropriate metabolic regulation, riboswitches must discriminate efficiently between their target ligands and chemically similar molecules that are also present in the cell. A remarkable example of efficient ligand discrimination is a synthetic neomycin-sensing riboswitch. Paromomycin, which differs from neomycin only by the substitution of a single amino group with a hydroxy group, also binds but does not flip the riboswitch. Interestingly, the solution structures of the two riboswitch-ligand complexes are virtually identical. In this work, we demonstrate that the local loss of key intermolecular interactions at the substitution site is translated through a defined network of intramolecular interactions into global changes in RNA conformational dynamics. The remarkable specificity of this riboswitch is thus based on structural dynamics rather than static structural differences. In this respect, the neomycin riboswitch is a model for many of its natural counterparts.

The one and only fold? Three chemically synthesized μ‐conotoxin PIIIA isomers (see picture), which contain different disulfide connectivity, block the skeletal muscle voltage‐gated sodium channel NaV1.4 with similar, yet distinguishable potency. Hence, bioactivity of this μ‐conotoxin is not strictly coupled to its native fold. Future development of conotoxin‐derived analgesics may benefit from such a widened structural repertoire.

Disulfide bridges establish a fundamental element in the molecular architecture of proteins and peptides which are involved e.g., in basic biological processes or acting as toxins. NMR spectroscopy is one method to characterize the structure of bioactive compounds including cystine-containing molecules. Although the disulfide bridge itself is invisible in NMR, constraints obtained via the neighboring NMR-active nuclei allow to define the underlying conformation and thereby to resolve their functional background. In this mini-review we present shortly the impact of cysteine and disulfide bonds in the proteasome from different domains of life and give a condensed overview of recent NMR applications for the characterization of disulfide-bond containing biomolecules including advantages and limitations of the different approaches.