Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A tail fiber of phage T3 is a trimer of the product of gene 17 (gp17). Treatment of T3 phage particles with chymotrypsin resulted in cleavage of only the tail fiber protein, at a site near the distal end of the fiber, causing a decrease of about 10% in the size of gp17 in the treated virion. The N-terminal amino acid sequences of intact and cleaved tail fiber proteins were identical and corresponded to that deduced from the nucleotide sequence of gene 17 except for the absence of the initiation Met residue. These results indicate that cleavage of the tail fiber occurred near the C terminus and suggest that gp17 polypeptides are oriented parallel to each other in the tail fiber. Association of tail fibers with the tail involves the N-terminal region of gp17. Under mild conditions of SDS-polyacrylamide gel electrophoresis, intact tail fibers dissociated from virions but cleaved ones did not. The nucleotide sequences indicate that T3 and T7 gp17 contain many sites that are potentially sensitive to chymotrypsin. In fact, free tail fibers, purified from T3-infected cells, were cleaved to many smaller fragments by chymotrypsin. These results suggest that the attachment of the tail fibers to the tail may induce a change(s) in the configuration and/or arrangement of gp17 to mask the sensitive sites from cleavage by chymotrypsin.
 ...
PMID:Subunit arrangement of the tail fiber of bacteriophage T3. 294 77

During the morphogenesis of the bacteriophage T4 capsid, a conformational change of the major head shell protein, gene product (gp) 23, causes a 50% increase in capsid volume. This expansion is required to accept the full length chromosome and, therefore, must precede the completion of packaging. The expanded shell is thinner and more stable than its precursor, and can bind accessory proteins which further stabilize it. In phages lambda, T3, T7 and P22, expansion occurs during DNA packaging. However, in T4, expanded capsids can package DNA in vitro and expansion occurs in cells infected with packaging-defective mutants, raising the possibility that expansion and packaging are not coupled. Proteolytically mature gp23 (gp23*) in unexpanded proheads is sensitive to chymotrypsin cleavage at Phe154-Ser155, creating a 38 kDa peptide, while gp23* in expanded capsids is refractory to the protease. We used an expansion assay based on this protease sensitivity to determine the expansion status of capsids isolated from various packaging-defective mutants with the goal of determining whether packaging and expansion are normally linked. In infections at 20 degrees C, mutants in the packaging enzymes gp16 and gp17 fail to expand. However, in gene 49(-) mutants, which initiate packaging but fail to complete it, expansion is complete. Thus, packaging drives expansion, and the unexpanded prohead is the substrate for the packaging reaction. We also show that expansion observed in 16(-) and 17(-) infections at 37 degrees C is linked to aberrant packaging. Capsids produced at 15 minutes, when no packaging can be detected, never expand. However, by 35 minutes when aberrant packaging begins, so does expansion of freshly made capsids. Thus in all cases now examined, expansion is only observed in vivo when DNA packaging is also occurring, indicating that these two processes are coupled.
 ...
PMID:The bacteriophage T4 DNA packaging apparatus targets the unexpanded prohead. 982 5