Biomedical subjects

Marina Ramírez-Alvarado

Publications and source records attributed to Marina Ramírez-Alvarado.

4 recordsLinked to original sources

PubMed2004

Analysis of somatic hypermutation and antigenic selection in the clonal B cell in immunoglobulin light chain amyloidosis (AL).

Light chain amyloidosis (AL) is a protein folding disorder with an underlying B cell neoplasia where the monoclonal immunoglobulin light chains (LCs) produced from insoluble amyloid fibrils. The deposition of these fibrillar aggregates in vital organs causes severe organ dysfunction over time and is associated with high mortality. We have identified the postgerminal center status of the B cell clone by evaluating the presence of somatic hypermutation in the variable region of the LC gene in 27 (13 of the lambda and 14 of the kappa subtype) AL patients. Seven of the 27 clones showed statistically significant evidence of antigenic selection, using a multinomial algorithm. The framework region mutations were selected for conservation of protein structure in 13 of the 27 patients. Additionally, mutational clusterspots were identified at specific positions in the nucleotide and deduced protein sequence that could potentially contribute to destabilizing interactions resulting in a propensity to form amyloid.

Algorithms↗

PubMed2003

A general model for amyloid fibril assembly based on morphological studies using atomic force microscopy.

Based on atomic force microscopy analysis of the morphology of fibrillar species formed during fibrillation of alpha-synuclein, insulin, and the B1 domain of protein G, a previously described model for the assembly of amyloid fibrils of immunoglobulin light-chain variable domains is proposed as a general model for the assembly of protein fibrils. For all of the proteins studied, we observed two or three fibrillar species that vary in diameter. The smallest, protofilaments, have a uniform height, whereas the larger species, protofibrils and fibrils, have morphologies that are indicative of multiple protofilaments intertwining. In all cases, protofilaments intertwine to form protofibrils, and protofibrils intertwine to form fibrils. We propose that the hierarchical assembly model describes a general mechanism of assembly for all amyloid fibrils.

Amyloid↗

PubMed2003

Mutations in the B1 domain of protein G that delay the onset of amyloid fibril formation in vitro.

We previously reported that under certain experimental conditions, many variants of the B1 domain of IgG-binding protein G from Streptococcus form fibrils reproducibly. The variant I6T53 was the focus of the present study because the lag phase in the kinetics of fibril formation by this variant is significantly longer than that of other variants. This lag phase is distinguished by changes in both intrinsic fluorescence intensity and in light scattering of the protein. NMR diffusion measurements suggest that the soluble protein during the lag phase is monomeric. The kinetic profiles of fibril formation are found to depend on experimental conditions. The first kinetic phase diminishes almost completely when the reaction is seeded with preformed amyloid fibrils.

Amyloid↗

PubMed2002

Does the location of a mutation determine the ability to form amyloid fibrils?

We have previously reported studies of fibril formation by a set of protein G B1 domain (beta1) variants, with mutations located around the central parallel beta-strands. In this study, we designed multiple mutations in the edge strands of beta1 to create proteins with a stability range comparable to that of the set of central mutants. All the edge variants are able to form amyloid fibrils when they are incubated at their melting temperatures. This result suggests that overall protein stability is the key determinant for amyloid formation and not the specific location of destabilizing mutations. The edge strand and variants cross-seed with each other and with members of the central variant family. Interesting fibrillar morphology was observed in some cross-seeding cases and its implications for a better understanding of nucleation and elongation events are discussed.

Amyloid↗