Bacteriophage barrels

One of the most striking results that has emerged from the high-resolution crystallographic studies of these icosahedral viruses is that their coat proteins have the same basic core structure, that of a jelly roll barrel, which was discussed in Chapter 5. This is true of plant, insect, and mammalian viruses. In the case of the picornaviruses, VPl, VP2, and VP3 all have the same jelly roll structure as the subunits of satellite tobacco necrosis virus, tomato bushy stunt virus, and the other T = 3 plant viruses. Not every spherical virus has subunit structures of the jelly roll type. As we will see, the subunits of the RNA bacteriophage, MS2, and those of alphavirus cores have quite different structures, although they do form regular icosahedral shells. 

Back Propagation Bacterial Toxins Bacteriophage Barbiturates Baroreceptor Reflex (3 Barrel... 

The stability of the /3-barrel itself was demonstrated in engineering experiments with OmpA. The four external loops of OmpA were replaced by shortcuts in all possible combinations (Koebnik, 1999). The resulting deletion mutants lost their biological functions in bacterial / -conjugation and as bacteriophage receptors, but kept the transmembrane /1-barrel as demonstrated by their resistance to proteolysis and thermal denaturation. The results confirm the expectation that the large external loops do not contribute to /1-barrel folding and stability. 

FIGURE 1. Three-dimensional structure of catalytic core regions in Escherichia coli class I (A) and bacteriophage T4 class III (B) RNRs (Logan et ai, 1999 Uhlin and Eklund, 1994). The ten-stranded p/a barrel comprising the active site region is shown. The finger-loop, which contains the active site cysteine, is shown as a solid line. 

P2 (left) domains are antiparallel eight-stranded fi barrels. The connecting domain and intertwined loops hold them together. The coloring of both jelly-roll domains is as in Fig. 1. (b) The P3 m or capsid protein of bacteriophage PRDl (Benson et al, 1999) with the same coloring scheme, (c) The knob domain of the adenovirus fiber (van Raaij et al, 1999b). (d) Part of the trimeric adenovirus type 2 fiber, vdth 4 of the 15-residue repeats (total, 22 in this strain). 

---