Aquaporins (AQPs) are among the best structural-characterized membrane proteins, fulfilling the role of allowing water flux across cellular membranes. Thus far, 34 single amino acid polymorphisms have been reported in HUMSAVAR for human aquaporins as disease-related. They affect AQP2, AQP5 and AQP8, where they are associated with nephrogenic diabetes insipidus, keratoderma and colorectal cancer, respectively. For half of these mutations, although they are mostly experimentally characterized in their dysfunctional phenotypes, a structural characterization at a molecular level is still missing. In this work, we focus on such mutations and discuss what the structural defects are that they appear to cause. To achieve this aim, we built a 3D molecular model for each mutant and explored the effect of the mutation on all of their structural features. Based on these analyses, we could collect the structural defects of all the pathogenic mutations (here or previously analysed) under few main categories, that we found to nicely correlate with the experimental phenotypes reported for several of the analysed mutants. Some of the structural analyses we present here provide a rationale for previously experimentally observed phenotypes. Furthermore, our comprehensive overview can be used as a reference frame for the interpretation, on a structural basis, of defective phenotypes of other aquaporin pathogenic mutants.

We report here the rational design, synthesis and structural characterization in the solid state and in solution of the most potent and selective peptide-based Neurokinin A (NKA) antagonist, thus far described. We predicted the bioactive conformation of the known NKA antagonist cyclo(-Met¹-Gln²-Trp³-Phe⁴-Gly⁵-Leu⁶-) by comparison with the known structures of other cyclohexapeptides. On this basis we designed a highly constrained peptide molecule corresponding to a bicyclic hexapeptide containing two rings of 14 atoms, namely cyclo(-Met¹-Asp²-Trp³-Phe⁴-Dap⁵-Leu⁶-)cyclo(2β-5β). It was synthesized efficiently, using a combined solution and solid phase strategy. We fully characterized this molecule in the solid state by X-ray diffraction and we show that it adopts an almost identical conformation in acetonitrile solution by NMR spectroscopy. This structure fully confirms our hypothetical model. Its structure and conformational rigidity in solution explain the high potency and selectivity and the resistance to proteolytic degradation. Therefore the structural requirements for NKA antagonistic activity are clarified.

Worldwide, over 20 million patients suffer from bone disorders annually. Bone scaffolds are designed to integrate into host tissue without causing adverse reactions. Recently, chitosan, an easily available natural polymer, has been considered a suitable scaffold for bone tissue growth as it is a biocompatible, biodegradable, and non-toxic material with antimicrobial activity and osteoinductive capacity. In this work, chitosan was covalently and selectively biofunctionalized with two suitably designed bioactive synthetic peptides: a Vitronectin sequence (HVP) and a BMP-2 peptide (GBMP1a). Nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) investigations highlighted the presence of the peptides grafted to chitosan (named Chit-HVP and Chit-GBMP1a). Chit-HVP and Chit-GBMP1a porous scaffolds promoted human osteoblasts adhesion, proliferation, calcium deposition, and gene expression of three crucial osteoblast proteins. In particular, Chit-HVP highly promoted adhesion and proliferation of osteoblasts, while Chit-GBMP1a guided cell differentiation towards osteoblastic phenotype.