Ken-ichi Takahashi

AS-ALPS: a database for analyzing the effects of alternative splicing on protein structure, interaction and network in human and mouse

We have constructed a database, AS-ALPS (alternative splicing-induced alteration of protein structure), which provides information that would be useful for analyzing the effects of alternative splicing (AS) on protein structure, interactions with other bio-molecules and protein interaction networks in human and mouse. Several AS events have been revealed to contribute to the diversification of protein structure, which results in diversification of interaction partners or affinities, which in turn contributes to regulation of bio-molecular networks. Most AS variants, however, are only known at the sequence level. It is important to determine the effects of AS on protein structure and interaction, and to provide candidates for experimental targets that are relevant to network regulation by AS. For this purpose, the three-dimensional (3D) structures of proteins are valuable sources of information; however, these have not been fully exploited in any other AS-related databases. AS-ALPS is the only AS-related database that describes the spatial relationships between protein regions altered by AS (‘AS regions’) and both the proteins’ hydrophobic cores and sites of inter-molecular interactions. This information makes it possible to infer whether protein structural stability and/or protein interaction are affected by each AS event. AS-ALPS can be freely accessed at http://as-alps.nagahama-i-bio.ac.jp and http://genomenetwork.nig.ac.jp/as-alps/.

AS-EAST

Summary: Alternative Splicing Effects ASsessment Tools (AS-EAST) is an online tool for the functional annotation of putative proteins encoded by transcripts generated by alternative splicing (AS). When provided with a transcript sequence, AS-EAST identifies regions altered by AS events in the putative protein sequence encoded by the transcript. Users can evaluate the predicted function of the putative protein by inspecting whether functional domains are included in the altered regions. Moreover, users can infer the loss of inter-molecular interactions in the protein network according to whether the AS events affect interaction residues observed in the 3D structure of the reference isoform. The information obtained from AS-EAST will help to design experimental analyses for the functional significance of novel splice isoforms. Availability: The online tool is freely available at http://as-alps.nagahama-i-bio.ac.jp/ASEAST/. Contact: m_shionyu@nagahama-i-bio.ac.jp

Retention of local conformational compactness in unfolding of barnase; Contribution of end-to-end interactions within quasi-modules

To understand how protein reduces the conformational space to be searched for the native structure, it is crucial to characterize ensembles of conformations on the way of folding processes, in particular ensembles of relatively long-range structures connecting between an extensively unfolded state and a state with a native-like overall chain topology. To analyze such intermediate conformations, we performed multiple unfolding molecular dynamics simulations of barnase at 498K. Some short-range structures such as part of helix and turn were well sustained while most of the secondary structures and the hydrophobic cores were eventually lost, which is consistent with the results by other experimental and computational studies. The most important novel findings were persistence of long-range relatively compact substructures, which was captured by exploiting the concept of module. Module is originally introduced to describe the hierarchical structure of a globular protein in the native state. Modules are conceptually such relatively compact substructures that are resulted from partitioning the native structure of a globular protein completely into several contiguous segments with the least extended conformations. We applied this concept of module to detect a possible hierarchical structure of each snapshot structure in unfolding processes as well. Along with this conceptual extension, such detected relatively compact substructures are named quasi-modules. We found almost perfect persistence of quasi-module boundaries that are positioned close to the native module boundaries throughout the unfolding trajectories. Relatively compact conformations of the quasi-modules seemed to be retained mainly by hydrophobic interactions formed between residues located at both terminal regions within each module. From these results, we propose a hypothesis that hierarchical folding with the early formation of quasi-modules effectively reduces search space for the native structure.

Intramolecular complementation of measles virus fusion protein stability confers cell–cell fusion activity at 37 °C

The fusion (F) protein of measles virus mediates membrane fusion. In this study, we investigated the molecular basis of the cell–cell fusion activity of the F protein. The N465H substitution in the heptad repeat B domain of the stalk region of the F protein eliminates this activity, but an additional mutation in the DIII domain of the head region – N183D, F217L, P219S, I225T or G240R – restores cell–cell fusion. Thermodynamically stabilized by the N465H substitution, the F protein required elevated temperature as high as 40 °C to promote cell–cell fusion, whereas all five DIII mutations caused destabilization of the F protein allowing the highest fusion activity at 30 °C. Stability complementation between the two domains conferred an efficient cell–cell fusion activity on the F protein at 37 °C.

A residue located at the junction of the head and stalk regions of measles virus fusion protein regulates membrane fusion by controlling conformational stability

The fusion (F) protein of measles virus performs refolding from the thermodynamically metastable prefusion form to the highly stable postfusion form via an activated unstable intermediate stage, to induce membrane fusion. Some amino acids involved in the fusion regulation cluster in the heptad repeat B (HR-B) domain of the stalk region, among which substitution of residue 465 by various amino acids revealed that fusion activity correlates well with its side chain length from the Cα (P<0.01) and van der Waals volume (P<0.001), except for Phe, Tyr, Trp, Pro and His carrying ring structures. Directed towards the head region, longer side chains of the non-ring-type 465 residues penetrate more deeply into the head region and may disturb the hydrophobic interaction between the stalk and head regions and cause destabilization of the molecule by lowering the energy barrier for refolding, which conferred the F protein enhanced fusion activity. Contrarily, the side chain of ring-type 465 residues turned away from the head region, resulting in not only no contact with the head region but also extensive coverage of the HR-B surface, which may prevent the dissociation of the HR-B bundle for initiation of membrane fusion and suppress fusion activity. Located in the HR-B domain just at the junction between the head and stalk regions, amino acid 465 is endowed with a possible ability to either destabilize or stabilize the F protein depending on its molecular volume and the direction of the side chain, regulating fusion activity of measles virus F protein.