Estimation of the secondary structure of protein A from S. aureus by CD-spectroscopy

Mechanism of antibodies purification by protein A

Protein A, a major cell wall component of Staphylococcus aureus, is one of the first immunoglobulin-binding proteins that is discovered about 80 years ago. However, a great deal of development in both purification methods and application of antibodies in treatment have been done. There are many publications based on the untargeted (size exclusion, ion exchange and hydrophobic interactions) and targeted (affinity) methods by scientists in academic/industry groups. In this review, we have focused on the study of both native and engineered Protein A to understand its mechanism in the purification of antibodies. What domain of Protein A dose interact with antibody? Where are contact regions? What is the non-covalent interaction mechanism of Protein A and antibody? Does alkaline condition, in the washing step, influence on antibody structure and activity? On the other hand, the immobilization of Protein A on various sorbents such as agarose, silica, polysaccharide, polymers, and magnetic nanoparticles have investigated. Also, the application of Protein A as biosensor for detection of the antibody is discussed. We have tried to find interesting and stimulating answers to all these questions.

A stereocomplex platform efficiently detecting antigen-antibody interactions

Ultrathin poly(methyl methacrylate) (PMMA) stereocomplex films with macromolecularly double-stranded regular nanostructures were prepared by layer-by-layer assembly of isotactic and syndiotactic PMMAs on solid surfaces. Antibodies were immobilized through the Fc region-capturing protein A, which had been physically adsorbed on the complex film, and the binding of antigens to immobilized antibodies was quantitatively investigated by the quartz crystal microbalance technique. Greater amounts of protein A with native forms were adsorbed on the complex film than those on conventional single-component PMMA films. Antibodies with high target-binding activities were also immobilized on the complex film. A greater amount of antigens could be detected on the complex film. The activity of protein A was maintained on the complex for a long time even within a dried state. The mechanism for the preservation of protein native forms on the complex surface was speculated by analyzing the physical adsorption of proteins with various secondary structures. Stereocomplex films can be utilized as novel coating nanomaterials for efficiently detecting protein-protein interactions.

The secondary structure of protein G', a robust molecule

The secondary structure of recombinant streptococcal Protein G' was predicted and compared with spectropolarimetric data. The predicted secondary structure consisted of 37 +/- 4% alpha-helix and 30 +/- 5% beta-sheet, whereas the values obtained from c.d. data were 29 +/- 2% alpha-helix and 41 +/- 3% beta-sheet. An alpha-helix-beta-sheet/turn-alpha-helix motif is conjectured to comprise the Fc-binding unit. The c.d. spectra in the near u.v. and far u.v. show that the Protein G' molecule is stable to heating at 100 degrees C and to extremes of pH (pH 1.5 to 11.0). The protein retained biological activity at these extremes. The molecule uncoils above pH 11.5 in a time-dependent fashion. Unfolding of the molecule in guanidinium chloride was monitored by c.d. and fluorescence emission; 3 M-guanidinium chloride was required to unfold the protein by 50%. The protein was completely unfolded in 5.5 M-guanidinium chloride and fully refolded with restoration of activity after removal of guanidinium chloride.

Staphylococcal protein A consists of five IgG-binding domains

A genetic approach is described to clarify the IgG-binding properties of the N-terminal portion of staphylococcal protein A (region E). Several gene fragments, encoding region E or B or protein A, have been cloned and expressed in Escherichia coli. The gene products were purified by IgG-affinity chromatography and subjected to structural and functional analyses. Both fragments can be efficiently purified using this method, suggesting that region B as well as region E has Fc-binding activity. In addition, gene fusions were assembled giving fragments EB and EE, which both showed a divalent Fc-binding. These results demonstrate that protein A consists of five IgG-binding domains. The implications of these findings for the structure of protein-A--immunoglobulin-G complexes are discussed.

Region X, the cell-wall-attachment part of staphylococcal protein A

The sequence of region X of staphylococcal protein A has been determined. The hypothesis has been put forward that this region spans the Staphylococcus aureus cell wall and is responsible for the binding to the peptidoglycan. The primary amino acid sequence of region X was determined for two strains exhibiting cell-wall-bound protein A, Cowan I and 8325-4. The sequence determination of the Cowan I material is partial and was performed by Edman degradation, in contrast to the sequence of the 8325-4 material which was completely analyzed by nucleotide sequencing of the corresponding gene. The region consists of two structurally different domains, a highly repetitive region (Xr), with an octapeptide structure repeated approximately 12 times, and a C-terminal domain (Xc) with an unique sequence. A comparison between the two strains reveals a high mutual homology as well as a high internal homology between the octapeptide structures. Six out of eight amino acids are identical in the repetition of this structure throughout region Xr in both proteins and the other two are changed in a rather regular pattern.

Binding of immunoglobulins to protein A and immunoglobulin levels in mammalian sera

The use of protein A from S. aureus (SpA) as an anti-IgG reagent in immunological techniques has extended in recent years, together with knowledge about its interaction with immunoglobulins of different species. Current data with respect to the binding of protein A to immunoglobulins and to the levels of immunoglobulins in the sera of some mammalian species are reviewed.