Aquaporin (AQP) 4 is the predominant water channel in the mammalian brain, abundantly expressed in the blood-brain and braincerebrospinal fluid interfaces of glial cells. Its function in cerebral water balance has implications in neuropathological disorders, including brain edema, stroke, and head injuries. The 1.8-Å crystal structure reveals the molecular basis for the water selectivity of the channel. Unlike the case in the structures of water-selective AQPs AqpZ and AQP1, the asparagines of the 2 Asn-Pro-Ala motifs do not hydrogen bond to the same water molecule; instead, they bond to 2 different water molecules in the center of the channel. Molecular dynamics simulations were performed to ask how this observation bears on the proposed mechanisms for how AQPs remain totally insulating to any proton conductance while maintaining a single file of hydrogen bonded water molecules throughout the channel.brain edema ͉ inhibitor discovery ͉ NPA motif

Significance mAbs are increasingly being used for treatment of chronic diseases wherein the subcutaneous delivery route is preferred to enable self-administration and at-home use. To deliver high doses (several hundred milligrams) through a small volume (∼1 mL) into the subcutaneous space, mAb solutions need to have low viscosity. Concomitantly, acceptable chemical stability is required for adequate shelf life, and normal in vivo clearance is needed for less frequent dosing. We propose in silico tools that provide rapid assessment of atypical behavior of mAbs (high viscosity, chemical degradation, and fast plasma clearance), which are simply predicted from sequence and/or structure-derived parameters. Such analysis will greatly improve the probability of success to move mAb-based therapeutics efficiently into clinical development and ultimately benefit patients.

Isaac has an open source license and can be obtained at https://github.com/sequencing.

Post-translational phosphorylation plays a key role in regulating protein function. Here, we provide a quantitative assessment of the relative strengths of hydrogen bonds involving phosphorylated amino acid side chains (pSer, pAsp) with several common donors (Arg, Lys, and backbone amide groups). We utilize multiple levels of theory, consisting of explicit solvent molecular dynamics, implicit solvent molecular mechanics, and quantum mechanics with a self-consistent reaction field treatment of solvent. Because the approximately 6 pKa of phosphate suggests that -1 and -2 charged species may coexist at physiological pH, hydrogen bonds involving both protonated and deprotonated phosphates for all donor-acceptor pairs are considered. Multiple bonding geometries for the charged-charged interactions are also considered. Arg is shown to be capable of substantially stronger salt bridges with phosphorylated side chains than Lys. A pSer hydrogen-bond acceptor tends to form more stable interactions than a pAsp acceptor. The effect of phosphate protonation state on the strengths of the hydrogen bonds is remarkably subtle, with a more pronounced effect on pAsp than on pSer.