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The Major Cell Envelope Protein of Micrococcus radiodurans (R1)

1982; Wiley; Volume: 125; Issue: 3 Linguagem: Inglês

10.1111/j.1432-1033.1982.tb06715.x

1432-1033

Wolfgang Baumeister, Franck Hugues Karrenberg, Reinhard Rachel, Andreas Engel, B. ten Heggeler, W. O. Saxton,

Enzyme Structure and Function

The so‐called HPI layer, representing the major cell envelope protein of the radiotolerant bacterium Micrococcus radiodurans , is a hexagonally patterned macromolecular monolayer; it is intimately associated with the outer membraneous layer (‘backing layer’) of the bacterium and covers its surface completely. By virtue of its quite unusual resistance to chemical perturbants it can easily be isolated, e.g. by detergent extraction of whole cells. A detailed description of the morphology of the HPI layer protein is given (resolution 1.8 nm), based on electron microscopy and image processing. Infrared spectroscopy shows that the secondary structure of the protein is stable under a wide range of environmental conditions; a considerable portion (30%) of the protein exists in the form of B structure. Direct mass measurements in a scanning transmission electron microscope reveal that the HPI layer protein has a molecular mass of approximately 655 kDa. Although masked by extensive proteolytic cleavage it appears that the morphologicaI protein units are composed of six identical protomers. All evidence accumulated so far supports our view that proteolysis is not a preparation artifact, but occurs already in vivo , without affecting the physical structure of the protein.