Neuronal nicotinic acetylcholine receptors (nAChRs) are a family of pentameric, ligand-gated ion channels that are located on the surface of neurons and non-neuronal cells and have multiple physiological and pathophysiological functions. In order to reach the cell surface, many nAChR subtypes require the help of chaperone and/or auxiliary/accessory proteins for their assembly, trafficking, pharmacological modulation, and normal functioning in vivo. The use of powerful genome-wide cDNA screening has led to the identification and characterisation of the molecules and mechanisms that participate in the assembly and trafficking of receptor subtypes, including chaperone and auxiliary or accessory proteins. The aim of this review is to describe the latest findings concerning nAChR chaperones and auxiliary proteins and pharmacological chaperones, and how some of them control receptor biogenesis or regulate channel activation and pharmacology. Some auxiliary proteins are subtype selective, some regulate various subtypes, and some not only modulate nAChRs but also target other receptors and signalling pathways. We also discuss how changes in auxiliary proteins may be involved in nAChR dysfunctions.

Chitin, a natural polymer of N-acetylglucosamine chains, is a principal component of the apical extracellular matrix in arthropods. Chitin microfibrils serve as structural components of natural biocomposites present in the extracellular matrix of a variety of invertebrates including sponges, molluscs, nematodes, fungi and arthropods. In this review, we summarize the frontier advances of insect chitin synthesis. More specifically, we focus on the chitin synthase (CHS), which catalyzes the key biosynthesis step. CHS is also known as an attractive insecticidal target in that this enzyme is absent in mammals, birds or plants. As no insect chitin synthase structure have been reported so far, we review recent studies on glycosyltransferase domain structures derived from fungi and oomycetes, which are conserved in CHS from all species containing chitin. Auxiliary proteins, which coordinate with CHS in chitin biosynthesis and assembly, are also discussed.

AMPA receptors mediate fast synaptic transmission in the CNS and can assemble with several types of auxiliary proteins in a spatio-temporal manner, from newly synthesized AMPA receptor tetramers to mature AMPA receptors in the cell membrane. As such, the interaction of auxiliary subunits with the AMPA receptor plays a major role in the regulation of AMPA receptor biogenesis, trafficking, and biophysical properties. Throughout the years, various \'families\' of proteins have been identified and today the approximate full complement of AMPAR auxiliary proteins is known. This review presents the current knowledge on the most prominent AMPA-receptor-interacting auxiliary proteins, highlights recent results regarding the Shisa protein family, and provides a discussion on future research that might contribute to the discovery of novel pharmacological targets of auxiliary subunits.

Glutamate receptor auxiliary proteins control receptor distribution and function, ultimately controlling synapse assembly, maturation, and plasticity. At the Drosophila neuromuscular junction (NMJ), a synapse with both pre- and postsynaptic kainate-type glutamate receptors (KARs), we show that the auxiliary protein Neto evolved functionally distinct isoforms to modulate synapse development and homeostasis. Using genetics, cell biology, and electrophysiology, we demonstrate that Neto-α functions on both sides of the NMJ. In muscle, Neto-α limits the size of the postsynaptic receptor field. In motor neurons (MNs), Neto-α controls neurotransmitter release in a KAR-dependent manner. In addition, Neto-α is both required and sufficient for the presynaptic increase in neurotransmitter release in response to reduced postsynaptic sensitivity. This KAR-independent function of Neto-α is involved in activity-induced cytomatrix remodeling. We propose that Drosophila ensures NMJ functionality by acquiring two Neto isoforms with differential expression patterns and activities.

Respiration on trimethylamine oxide (TMAO) allows bacterial survival under anoxia. In Shewanella oneidensis, Tor is the system involved in TMAO respiration and it is encoded by the torECAD operon. The torA and torC genes encode TorA terminal reductase and the TorC c-type cytochrome, respectively. Sequence analysis suggests that TorD is the putative specific chaperone of TorA, whereas TorE is of unknown function. The purpose of this study was to understand whether TorD and TorE are two accessory proteins that affect the efficiency of the Tor system by chaperoning TorA terminal reductase. Moreover, by deleting each gene, we established that the absence of TorD drastically affects the stability of TorA, while the absence of TorE does not affect TorA stability or activity. Since TMAO reduction was affected in the ΔtorE mutant, TorE could be an additional component of the TorC-TorA electron transfer chain during bacterial respiration. Finally, a fitness experiment indicated that the presence of TorE, as expected, confers a selective advantage in competitive environments.

Immunophilins occur in almost all living organisms. They are ubiquitously expressed proteins including cyclophilins, FK506/rapamycin-binding proteins, and parvulins. Their functional significance in vascular plants is mostly related to plant developmental processes, signalling, and regulation of photosynthesis. Enzymatically active immunophilins catalyse isomerization of proline imidic peptide bonds and assist in rapid folding of nascent proline-containing polypeptides. They also participate in protein trafficking and assembly of supramolecular protein complexes. Complex immunophilins possess various additional functional domains associated with a multitude of molecular interactions. A considerable number of immunophilins act as auxiliary and/or regulatory proteins in highly specialized cellular compartments, such as lumen of thylakoids. In this review, we present a comprehensive overview of so far identified chloroplast immunophilins that assist in specific assembly/repair processes necessary for the maintenance of efficient photosynthetic energy conversion.

The replication and pathogenicity of lentiviruses is crucially modulated by \"auxiliary proteins\" which are expressed in addition to the canonical retroviral ORFs gag, pol, and env. Strategies to inhibit the activity of such proteins are often sought and proposed as possible additions to increase efficacy of the traditional antiretroviral therapy. This requires the acquisition of an in-depth knowledge of the molecular mechanisms underlying their function. The Nef auxiliary protein is expressed uniquely by primate lentiviruses and plays an important role in virus replication in vivo and in the onset of AIDS. Among its several activities Nef enhances the intrinsic infectivity of progeny virions through a mechanism which remains today enigmatic. Here we review the current knowledge surrounding such activity and we discuss its possible role in HIV biology.