Protein domain boundary predictions: a structural biology perspective

Linkers: A synergistic way for the synthesis of chimeric proteins

In the cell, the protein domains are attached with the short oligopeptide, commonly known as linker peptide. Besides bridging, the linker assists in the domain-domain interaction and protein folding into the peculiar conformations. Linkers allow or control the movement of protein domains in the dynamic cellular environment. The recent advances in the recombinant DNA technology enable the construction of multiple gene constructs in an open reading frame. The express sequences can work in a cascade to cater for myriad functions. This trend has given momentum to incorporating bridge sequences (linker) that essentially separates the independent domains. According to the cellular need, the bridging partner can be spaced at a secure gap or requires attaching or interacting physically. The flexible or rigid linker can help to achieve such conformations in chimeric fusion proteins. The linker can improve solubility, proteolytic resistance and stability of such fusion proteins. Recently, linker aided protein switches and antibody-drug conjugates are gaining the attention of researchers worldwide. Here, we thoroughly reviewed the types of the linker, strategies for linker engineering and the composition of a linker.

ThreaDomEx: a unified platform for predicting continuous and discontinuous protein domains by multiple-threading and segment assembly

We develop a hierarchical pipeline, ThreaDomEx, for both continuous domain (CD) and discontinuous domain (DCD) structure predictions. Starting from a query sequence, ThreaDomEx first threads it through the PDB to identify multiple structure templates, where a profile of domain conservation score (DC-score) is derived for domain-segment assignment. To further detect DCDs that consist of separated segments along the sequence, a boundary-clustering algorithm is used to refine the DCD-linker locations. In case that the templates do not contain DCDs, a domain-segment assembly process, guided by symmetry comparison, is applied for further DCD detections. ThreaDomEx was tested a set of 1111 proteins and achieved a normalized domain overlap score of 89.3% compared to experimental data, which is significantly higher than other state-of-the-art methods. It also recalls 26.7% of DCDs with 72.7% precision on the proteins for which threading failed to detect any DCDs. The server provides facilities for users to interactively refine the domain models by adjusting DC-score threshold, deleting and adding domain linkers, and assembling domain segments, which are particularly helpful for the hard targets for which current methods have a low accuracy while human-expert knowledge and experimental insights can be used for refining models. ThreaDomEX server is available at http://zhanglab.ccmb.med.umich.edu/ThreaDomEx.