Abstract
Aquaporins are transmembrane channel proteins with key function being transportation of water or other small substrates. Escherichia coli Aqp Z transports water molecules only, whereas Glp F is permeable to glycerol. It is intriguing to explore the possibility to induce glycerol permeability in Aqp Z by targeted mutations. The Aqp Z mutants with mutated selectivity filter (SF) residues exhibit poor permeability for both glycerol and water. For addressing the complexity of protein systems, pair correlation information in protein sequence analyses is instructive to identify residues that are coupled by coevolution and motion. In this study, we analyze the correlation between residues and unravel the clustering patterns of coupled residues, beyond SF residues, in aquaglyceroporins (AQGPs). The identified coupled motifs are proposed to be sequenced into aquaporin (Aqp Z) to introduce glycerol permeability. These residues are located in the vicinity of SF region, C-loop, and M6–M7 linkage domain. Significant enlargement of SF pore size of the proposed Aqp Z mutant is observed by an all-atom replica exchange molecular dynamics simulation, which is critical to facilitate considerable glycerol passage as characterized in calculated free-energy landscapes. Clearly, the hidden connections among residues play crucial roles in water/glycerol selectivity. In contrast, single-site mutation-based scheme may even lead to undesirable effects in AQGPs, such as the blocking of water transportation by aromatic π-stacked gate. As demonstrated in this work, the pair correlation analysis guided rational mutagenesis provides a feasible strategy to modulate proteins’ functions.
Highlights
Aquaporin is a subfamily of transmembrane channel proteins, which belongs to the major intrinsic proteins.[1]
A data set of 305 bacterial aquaporin protein sequences treated after multiple sequence alignments was constructed based on previous work by Lin et al.[33]
The positions of these residues are represented by their position to the corresponding residues in aquaporin Z (Aqp Z) and glycerol facilitator protein F (Glp F), the two representative structures of AQP and AQGP
Summary
Aquaporin is a subfamily of transmembrane channel proteins, which belongs to the major intrinsic proteins.[1] They widely exist in most of prokaryotic and eukaryotic organisms.[2] The main function of aquaporins is the selective permeation of water and other small substrate across the biological membrane. Orthodox aquaporins (referred to as AQPs) are exclusively permeable to water, whereas the aquaglyceroporins (referred to as AQGPs) or glycerol facilitator proteins (GLPs) are permeable to both water and glycerol. Since the determination of the crystal structure of aquaporin 1 in 2000,2 more structures belonging to the aquaporin family have been determined in the last two decades.[3−6] Aquaporins play crucial roles in water transportation in metabolic pathways. Clinical and therapeutic studies have established the intimate correlation between aquaporin-deficient mutations in particular sites and various diseases, including cataracts,[7] nephrogenic diabetes insipidus,[8] Alzheimer’s disease,[9,10] and Parkinson’s disease.[11]
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