Identification of two antibody-interaction sites on the surface of Panulirus interruptus hemocyanin

Quantitative fitting of atomic models into observed densities derived by electron microscopy

A new methodology for fitting atomic models into density distributions is described. This approach is based on a global density correlation analysis that can be optionally supplemented by biochemical as well as biophysical data. The procedure is completely general and enables an objective evaluation of the resulting docking in the light of available biochemical and biophysical information as well as density correlation alone. In this paper we describe the implementation of the algorithm and its application to two biological systems. In both cases the procedure provided an interface model on the atomic level and located parts of the structure that were missing in the atomic model but present in the electron-microscopic construct. It also detected and quantified conformational changes in actomyosin complexes.

Influence of antibody binding on oxygen binding behavior of Panulirus interruptus hemocyanin

Oxygen binding behavior of monomeric subunit a and the hexameric form of this subunit of hemocyanin of Panulirus interruptus is influenced by the binding of various monoclonal antibodies. These antibodies react with other surface parts of the subunit than its second domain in which the oxygen binding site is located. The influence of three monoclonal antibodies and their antigen binding fragments (Fab) has been investigated. Two antibodies increase the oxygen affinity of monomeric hemocyanin from that observed in its low affinity T-state, while the third has little influence on this property. Fab fragments abolish almost completely the cooperativity of oxygen binding by the hexameric hemocyanin molecule. The two antibodies which increase the oxygen affinity of the monomeric molecule stabilize high-affinity states of the hexameric molecule, while the third stabilizes the low-affinity state.

Comparison of three methods for competitive binding of monoclonal antibodies. The localization of antigenic sites for monoclonal antibodies on Panulirus interruptus hemocyanin

The competitive binding of a panel of monoclonal antibodies against hemocyanin of Panulirus interruptus hemocyanin was investigated with three different methods. A competitive-binding immunoassay method was more successful in the determination of ternary complexes than gel electrophoresis and gel filtration. The latter two methods could only be applied with antibodies possessing a higher affinity. Eleven monoclonal antibodies were assigned to groups on the basis of their interactions with five antigenic regions.

Production and characterization of monoclonal antibodies against Panulirus interruptus hemocyanin

Since the primary and higher-order structures of hemocyanin from the crustacean arthropod Panulirus interruptus have been elucidated completely, it should be possible to determine which regions of this immunogenic molecule are recognized most often by antibodies. Monoclonal antibodies were raised against subunits a and b of this hemocyanin, and fourteen of them were further characterized. The produced antibodies were of class IgG, subclasses 1 or 2a. Most of them had dissociation constants on the order of magnitude 10(-8)-10(-10), a few had lower affinities. Most clones showed no or negligible cross-reactivity with other crustacean hemocyanins. The reactivity of most other clones diminished with increasing sequence difference between the investigated hemocyanins. However, in a few instances a stronger reactivity with other hemocyanins was observed than with that from Panulirus interruptus. After complete denaturation of the hemocyanin there was no reaction with the monoclonal antibodies, indicating that the latter recognize conformational epitopes. Only one monoclonal antibody reacted with denatured hemocyanin. This antibody was also the only one which reacted with a CNBr digest, which means that it recognizes a sequential epitope. Several antibodies showed a faint reaction on Western blots, indicating the presence of some refolded native structure. Limited proteolysis of the hemocyanin molecule results in the formation of a 18 kDa fragment, representing domain 1, and a 55 kDa fragment representing domains 2 and 3. It was determined on Western blots of the digest on which fragment epitopes for eleven of the monoclonal antibodies were located.