Conformational switch of a flexible loop in human laminin receptor determines laminin-1 interaction

Discovery of new small molecules inhibiting 67 kDa laminin receptor interaction with laminin and cancer cell invasion

The 67 kDa laminin receptor (67LR) is a non-integrin receptor for laminin (LM) that derives from a 37 kDa precursor (37LRP). 67LR expression is increased in neoplastic cells and correlates with an enhanced invasive and metastatic potential. We used structure-based virtual screening (SB-VS) to search for 67LR inhibitory small molecules, by focusing on a 37LRP sequence, the peptide G, able to specifically bind LM. Forty-six compounds were identified and tested on HEK-293 cells transfected with 37LRP/67LR (LR-293 cells). One compound, NSC47924, selectively inhibited LR-293 cell adhesion to LM with IC50 and Ki values of 19.35 and 2.45 μmol/L. NSC47924 engaged residues W176 and L173 of peptide G, critical for specific LM binding. Indeed, NSC47924 inhibited in vitro binding of recombinant 37LRP to both LM and its YIGSR fragment. NSC47924 also impaired LR-293 cell migration to LM and cell invasion. A subsequent hierarchical similarity search with NSC47924 led to the identification of additional four compounds inhibiting LR-293 cell binding to LM: NSC47923, NSC48478, NSC48861, and NSC48869, with IC50 values of 1.99, 1.76, 3.4, and 4.0 μmol/L, respectively, and able to block in vitro cancer cell invasion. These compounds are promising scaffolds for future drug design and discovery efforts in cancer progression.

Force-induced globule-coil transition in laminin binding protein and its role for viral-cell membrane fusion

The specific interactions of the pairs laminin binding protein (LBP)-purified tick-borne encephalitis viral surface protein E and certain recombinant fragments of this protein, as well as West Nile viral surface protein E and certain recombinant fragments of that protein, are studied by combined methods of single-molecule dynamic force spectroscopy (SMDFS), enzyme immunoassay and optical surface waves-based biosensor measurements. The experiments were performed at neutral pH (7.4) and acid pH (5.3) conditions. The data obtained confirm the role of LBP as a cell receptor for two typical viral species of the Flavivirus genus. A comparison of these data with similar data obtained for another cell receptor of this family, namely human αVβ3 integrin, reveals that both these receptors are very important. Studying the specific interaction between the cell receptors in question and specially prepared monoclonal antibodies against them, we could show that both interaction sites involved in the process of virus-cell interaction remain intact at pH 5.3. At the same time, for these acid conditions characteristic for an endosome during flavivirus-cell membrane fusion, SMDFS data reveal the existence of a force-induced (effective already for forces as small as 30-70 pN) sharp globule-coil transition for LBP and LBP-fragments of protein E complexes. We argue that this conformational transformation, being an analog of abrupt first-order phase transition and having similarity with the famous Rayleigh hydrodynamic instability, might be indispensable for the flavivirus-cell membrane fusion process.

Novel insights into the function and dynamics of extracellular matrix in liver fibrosis

Emerging evidence suggests that altered components and posttranslational modifications of proteins in the extracellular matrix (ECM) may both initiate and drive disease progression. The ECM is a complex grid consisting of multiple proteins, most of which play a vital role in containing the essential information needed for maintenance of a sophisticated structure anchoring the cells and sustaining normal function of tissues. Therefore, the matrix itself may be considered as a paracrine/endocrine entity, with more complex functions than previously appreciated. The aims of this review are to 1) explore key structural and functional components of the ECM as exemplified by monogenetic disorders leading to severe pathologies, 2) discuss selected pathological posttranslational modifications of ECM proteins resulting in altered functional (signaling) properties from the original structural proteins, and 3) discuss how these findings support the novel concept that an increasing number of components of the ECM harbor signaling functions that can modulate fibrotic liver disease. The ECM entails functions in addition to anchoring cells and modulating their migratory behavior. Key ECM components and their posttranslational modifications often harbor multiple domains with different signaling potential, in particular when modified during inflammation or wound healing. This signaling by the ECM should be considered a paracrine/endocrine function, as it affects cell phenotype, function, fate, and finally tissue homeostasis. These properties should be exploited to establish novel biochemical markers and antifibrotic treatment strategies for liver fibrosis as well as other fibrotic diseases.

Looking into laminin receptor: critical discussion regarding the non-integrin 37/67-kDa laminin receptor/RPSA protein

The 37/67-kDa laminin receptor (LAMR/RPSA) was originally identified as a 67-kDa binding protein for laminin, an extracellular matrix glycoprotein that provides cellular adhesion to the basement membrane. LAMR has evolutionary origins, however, as a 37-kDa RPS2 family ribosomal component. Expressed in all domains of life, RPS2 proteins have been shown to have remarkably diverse physiological roles that vary across species. Contributing to laminin binding, ribosome biogenesis, cytoskeletal organization, and nuclear functions, this protein governs critical cellular processes including growth, survival, migration, protein synthesis, development, and differentiation. Unsurprisingly given its purview, LAMR has been associated with metastatic cancer, neurodegenerative disease and developmental abnormalities. Functioning in a receptor capacity, this protein also confers susceptibility to bacterial and viral infection. LAMR is clearly a molecule of consequence in human disease, directly mediating pathological events that make it a prime target for therapeutic interventions. Despite decades of research, there are still a large number of open questions regarding the cellular biology of LAMR, the nature of its ability to bind laminin, the function of its intrinsically disordered C-terminal region and its conversion from 37 to 67 kDa. This review attempts to convey an in-depth description of the complexity surrounding this multifaceted protein across functional, structural and pathological aspects.

The folded and disordered domains of human ribosomal protein SA have both idiosyncratic and shared functions as membrane receptors

The human RPSA [ribosomal protein SA; also known as LamR1(laminin receptor 1)] belongs to the ribosome but is also a membrane receptor for laminin, growth factors, prion, pathogens and the anticarcinogen EGCG (epigallocatechin-gallate). It contributes to the crossing of the blood–brain barrier by neurotropic viruses and bacteria, and is a biomarker of metastasis. RPSA includes an N-terminal domain, which is folded and homologous to the prokaryotic RPS2, and a C-terminal extension, which is intrinsically disordered and conserved in vertebrates. We used recombinant derivatives of RPSA and its N- and C-domains to quantify its interactions with ligands by in-vitro immunochemical and spectrofluorimetric methods. Both N- and C-domains bound laminin with K_D (dissociation constants) of 300 nM. Heparin bound only to the N-domain and competed for binding to laminin with the negatively charged C-domain, which therefore mimicked heparin. EGCG bound only to the N-domain with a K_D of 100 nM. Domain 3 of the envelope protein from yellow fever virus and serotypes-1 and -2 of dengue virus bound preferentially to the C-domain whereas that from West Nile virus bound only to the N-domain. Our quantitative in-vitro approach should help clarify the mechanisms of action of RPSA, and ultimately fight against cancer and infectious agents.

Extracellular matrix remodeling: the common denominator in connective tissue diseases. Possibilities for evaluation and current understanding of the matrix as more than a passive architecture, but a key player in tissue failure

Increased attention is paid to the structural components of tissues. These components are mostly collagens and various proteoglycans. Emerging evidence suggests that altered components and noncoded modifications of the matrix may be both initiators and drivers of disease, exemplified by excessive tissue remodeling leading to tissue stiffness, as well as by changes in the signaling potential of both intact matrix and fragments thereof. Although tissue structure until recently was viewed as a simple architecture anchoring cells and proteins, this complex grid may contain essential information enabling the maintenance of the structure and normal functioning of tissue. The aims of this review are to (1) discuss the structural components of the matrix and the relevance of their mutations to the pathology of diseases such as fibrosis and cancer, (2) introduce the possibility that post-translational modifications (PTMs), such as protease cleavage, citrullination, cross-linking, nitrosylation, glycosylation, and isomerization, generated during pathology, may be unique, disease-specific biochemical markers, (3) list and review the range of simple enzyme-linked immunosorbent assays (ELISAs) that have been developed for assessing the extracellular matrix (ECM) and detecting abnormal ECM remodeling, and (4) discuss whether some PTMs are the cause or consequence of disease. New evidence clearly suggests that the ECM at some point in the pathogenesis becomes a driver of disease. These pathological modified ECM proteins may allow insights into complicated pathologies in which the end stage is excessive tissue remodeling, and provide unique and more pathology-specific biochemical markers.