Various options are available for the treatment of chondral and osteochondral lesions of the knee and the ankle. Among the therapeutic options currently available, cell therapy systems can be ...considered consolidated procedures. Autologous chondrocytes implantation (ACI) was first proposed by Brittberg in 1994 as a method to treat chondral defects. To overcome the inconveniences of the first technique, a second generation ACI technique was developed. With this technique, the harvested chondrocytes are cultivated, expanded, and then seeded directly onto a biocompatible and biodegradable synthetic membrane. The arthroscopic ACI technique has been developed with the aim to reduce the morbidity of the open technique, to compete more closely with the other arthroscopic options of treatment. It was first described by Marcacci and coworkers in 2002 for the treatment of chondral defects of the knee. Instead Giannini and colleagues first described their experience with arthroscopic ACI in the ankle in 2008. Here, we describe the technique of the implantation of autologous chondrocytes, seeded on collagen membranes, fixed by fibrin glue by an all arthroscopic technique for the treatment of chondral lesions of the knee and the ankle.
Normal mode analysis is a widely used technique for reconstructing conformational changes of proteins from the knowledge of native structures. In this Letter, we investigate to what extent normal ...modes capture the salient features of the dynamics over a range of temperatures from close to T = 0 to above unfolding. We show that on the one hand, the use of normal modes at physiological temperatures is justified provided proteins are cooperative. On the other hand, it is imperative to consider several modes in order to eliminate the unpredictable temperature dependence of single- mode contributions to the protein fluctuations.
PDZ domains are typical examples of binding motifs mediating the formation of protein-protein assemblies in many different cells. A quantitative characterization of the mechanisms intertwining ...structure, chemistry and dynamics with the PDZ function represent a challenge in molecular biology. Here we investigated the influence of native state topology on the thermodynamics and the dissociation kinetics for a complex PDZ-peptide via Molecular Dynamics simulations based on a coarse-grained description of PDZ domains. Our native-centric approach neglects chemical details but incorporates the basic structural information to reproduce the protein functional dynamics as it couples to the binding. We found that at physiological temperatures the unbinding of a peptide from the PDZ domain becomes increasingly diffusive rather than thermally activated, as a consequence of the significant reduction of the free energy barrier with temperature. In turn, this results in a significant slowing down of the process of two orders of magnitude with respect to the conventional Arrhenius extrapolation from low temperature calculations. Finally, a detailed analysis of a typical unbinding event based on the rupture times of single peptide-PDZ contacts allows to shed further light on the dissociation mechanism and to elaborate a coherent picture of the relation between function and dynamics in PDZ domains.
PDZ (Post-synaptic density-95/discs large/zonula occludens-1) domains are
relatively small (80 to 120 residues) protein binding modules central in the
organization of receptor clusters and in the ...association of cellular proteins.
Their main function is to bind C-terminals of selected proteins that are
recognized through specific amino-acids in their carboxyl end. Binding is
associated with a deformation of the PDZ native structure and is responsible
for dynamical changes in regions not in direct contact with the target. We
investigate how this deformation is related to the harmonic dynamics of the PDZ
structure and show that one low-frequency collective normal mode, characterized
by the concerted movements of different secondary structures, is involved in
the binding process. Our results suggest that even minimal structural changes
are responsible of communication between distant regions of the protein, in
agreement with recent Nuclear Magnetic Resonance (NMR) experiments. Thus PDZ
domains are a very clear example of how collective normal modes are able to
characterize the relation between function and dynamics of proteins, and to
provide indications on the precursors of binding/unbonding events.
PDZ (Post-synaptic density-95/discs large/zonula occludens-1) domains are relatively small (80 to 120 residues) protein binding modules central in the organization of receptor clusters and in the ...association of cellular proteins. Their main function is to bind C-terminals of selected proteins that are recognized through specific amino-acids in their carboxyl end. Binding is associated with a deformation of the PDZ native structure and is responsible for dynamical changes in regions not in direct contact with the target. We investigate how this deformation is related to the harmonic dynamics of the PDZ structure and show that one low-frequency collective normal mode, characterized by the concerted movements of different secondary structures, is involved in the binding process. Our results suggest that even minimal structural changes are responsible of communication between distant regions of the protein, in agreement with recent Nuclear Magnetic Resonance (NMR) experiments. Thus PDZ domains are a very clear example of how collective normal modes are able to characterize the relation between function and dynamics of proteins, and to provide indications on the precursors of binding/unbonding events.
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