The α1 integrin cytoplasmic tail interacts with phosphoinositides and interferes with Akt activation

Integrin α1β1 is an adhesion receptor that binds to collagen and laminin. It regulates cell adhesion, cytoskeletal organization, and migration. The cytoplasmic tail of the α1 subunit consists of 15 amino acids and contains six positively charged lysine residues. In this study, we present evidence that the α1 integrin cytoplasmic tail (α1CT) directly associates with phosphoinositides, preferentially with phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). Since the association was disrupted by calcium, magnesium and phosphate ions, this interaction appears to be in ionic nature. Here, the peptide-lipid interaction was driven by the conserved KIGFFKR motif. The exchange of both two potential phospholipid-binding lysines for glycines in the KIGFFKR motif increased α1β1 integrin-specific adhesion and F-actin cytoskeleton formation compared to cells expressing the unmodified α1 subunit, whereas only mutation of the second lysine at position 1171 increased levels of constitutively active α1β1 integrins on the cell surface. In addition, enhanced focal adhesion formation and increased phosphorylation of focal adhesion kinase, but decreased phosphorylation of AKT was observed in these cells. We conclude that the KIGFFKR motif, and in particular lysine1171 is involved in the dynamic regulation of α1β1 integrin activity and that the interaction of α1CT with phosphoinositides may contribute to this process.

A meta-analysis on the levels of VILIP-1 in the CSF of Alzheimer's disease compared to normal controls and other neurodegenerative conditions

Alzheimer's disease (AD) is a progressing neurodegenerative disorder and the main cause of serious irreversible cognitive decline in elderly people. Visinin-like protein 1 (VILIP-1) is a member of the family of calcium-binding proteins and plays a crucial role in AD pathophysiology. Multiple studies have shown that CSF levels of VILIP-1 are increased in AD patients compared to normal controls, or other neurodegenerative conditions. We searched online databases for studies on the levels of VILIP-1 in the CSF of AD patients in comparison to normal controls, mild cognitive impairment (MCI) patients and Dementia with Lewy bodies (DLB) patients. A total of ten studies were used for the comparison between AD and controls, three studies for the comparison between AD and MCI, two studies for AD and DLB and two studies for the comparison between stable MCI and MCI progressed to AD. We found that VILIP-1 levels are significantly higher in AD compared to normal controls, but not to the other groups, and furthermore, they are significantly higher in patient with MCI progressed to AD, than in stable MCI patients.

Enhancing Top-Down Analysis Using Chromophore-Assisted Infrared Multiphoton Dissociation from (Phospho)peptides to Protein Assemblies

Infrared multiphoton dissociation (IRMPD) has been used in mass spectrometry to fragment peptides and proteins, providing fragments mostly similar to collisional activation. Using the 10.6 μm wavelength of a CO2 laser, IRMPD suffers from the relative low absorption cross-section of peptides and small proteins. Focusing on top-down analysis, we investigate different means to tackle this issue. We first reassess efficient sorting of phosphopeptides from nonphosphopeptides based on IR-absorption cross-sectional enhancement by phosphate moieties. We subsequently demonstrate that a myo-inositol hexakisphosphate (IP6) noncovalent adduct can substantially enhance IRMPD for nonphosphopeptides and that this strategy can be extended to proteins. As a natural next step, we show that native phospho-proteoforms of proteins display a distinct and enhanced fragmentation, compared to their unmodified counterparts, facilitating phospho-group site localization. We then evaluate the impact of size on the IRMPD of proteins and their complexes. When applied to protein complexes ranging from a 365 kDa CRISPR-Cas Csy ribonucleoprotein hetero-decamer, a 800 kDa GroEL homo-tetradecamer in its apo-form or loaded with its ATP cofactor, to a 1 MDa capsid-like homo-hexacontamer, we conclude that while phosphate moieties present in crRNA and ATP molecules enhance IRMPD, an increase in the IR cross-section with the size of the protein assembly also favorably accrues dissociation yields. Overall, our work showcases the versatility of IRMPD in the top-down analysis of peptides, phosphopeptides, proteins, phosphoproteins, ribonucleoprotein assemblies, and large protein complexes.

The Role of Visinin-Like Protein-1 in the Pathophysiology of Alzheimer's Disease

Calcium ions are crucial in the process of information transmission and integration in the central nervous system (CNS). These ions participate not only in intracellular mechanisms but also in intercellular processes. The changes in the concentration of Ca2 + ions modulate synaptic transmission, whereas neuronal activity induces calcium ion waves. Disturbed calcium homeostasis is thought to be one of the main features in the pathophysiology of Alzheimer's disease (AD), and AD pathogenesis is closely connected to Ca2 + signaling pathways. The effects of changes in neuronal Ca2 + are mediated by neuronal calcium sensor (NCS) proteins. It has been revealed that NCS proteins, with special attention to visinin-like protein 1 (VILIP-1), might have a connection to the etiology of AD. In the CNS, VILIP-1 influences the intracellular neuronal signaling pathways involved in synaptic plasticity, such as cyclic nucleotide cascades and nicotinergic signaling. This particular protein is implicated in calcium-mediated neuronal injury as well. VILIP-1 also participates in the pathological mechanisms of altered Ca2 + homeostasis, leading to neuronal loss. These findings confirm the utility of VILIP-1 as a useful biomarker of neuronal injury. Moreover, VILIP-1 plays a vital role in linking calcium-mediated neurotoxicity and AD-type pathological changes. The disruption of Ca2 + homeostasis caused by AD-type neurodegeneration may result in the damage of VILIP-1-containing neurons in the brain, leading to increased cerebrospinal fluid levels of VILIP-1. Thus, the aim of this overview is to describe the relationships of the NCS protein VILIP-1 with the pathogenetic factors of AD and neurodegenerative processes, as well as its potential clinical usefulness as a biomarker of AD. Moreover, we describe the current and probable therapeutic strategies for AD, targeting calcium-signaling pathways and VILIP-1.

Comparison of VILIP-1 and VILIP-3 binding to phospholipid monolayers

The neuronal calcium sensor proteins Visinin-like Proteins 1 (VILIP-1) and 3 (VILIP-3) are effectors of guanylyl cyclase and acetyl choline receptors, and transduce calcium signals in the brain. The “calcium-myristoyl” switch, which involves a post-translationally added myristoyl moiety and calcium binding, is thought to regulate their membrane binding capacity and therefore, play a critical role in their mechanism of action. In the present study, we investigated the effect of membrane composition and solvent conditions on the membrane binding mechanisms of both VILIPs using lipid monolayers at the air/buffer interface. Results based on comparison of the adsorption kinetics of the myristoylated and non-myristoylated proteins confirm the pivotal role of calcium and the exposed myristol moiety for sustaining the membrane-bound state of both VILIPs. However, we also observed binding of both VILIP proteins in the absence of calcium and/or myristoyl conjugation. We propose a two-stage membrane binding mechanism for VILIP-1 and VILIP-3 whereby the proteins are initially attracted to the membrane surface by electrostatic interactions and possibly by specific interactions with highly negatively charged lipids head groups. The extrusion of the conjugated myristoyl group, and the subsequent anchoring in the membrane constitutes the second stage of the binding mechanism, and ensures the sustained membrane-bound form of these proteins.