78-residue insertion

The subunit has a calculated molecular wdght of 103,916 including the acetyl group and the cofactor. The sequence is two residues longer at the amino-terminus and, similar to the bacterial enzyme, nine residues shorter at the carboxyl-terminus than the muscle enzyme when the two sequences are aligned for maximum matching (see below). Furthermore, there is a 78-residue insertion in the middle of the polypeptide chain of the type-L isozyme that occurs between residues... 

Functional Role of the 78-Residue Insertion in Type-L Isozyme... 

His residues in the peptide sequence are fundamental for Ni11 ion interactions with peptides. When the His residue is relatively distant from the N terminus, it may compete as a primary ligation site with the N-terminal amino nitrogen. However, even the higher number of His residues inserted inside the peptide sequence may be not able to compete with the albumin-like N terminus, unless the specific peptide structure is established. 

Bacteria generally have just one type of uracil DNA glycosylase, whereas humans have at least four types, with different specificities—an indicator of the importance of uracil removal from DNA. The most abundant human uracil glycosylase, UNG, is associated with the human replisome, where it eliminates the occasional U residue inserted in place of a T during replication. The deamination of C residues is 100-fold faster in single-stranded DNA than in double-stranded DNA, and... 

Amino-Terminal and Carboxyl-Terminal Modifications The first residue inserted in all polypeptides is Al-formylmethio-nine (in bacteria) or methionine (in eukaryotes). However, the formyl group, the amino-terminal Met residue, and often additional amino-terminal (and, in some cases, carboxyl-terminal) residues may be removed enzymatically in formation of the final functional protein. In as many as 50% of eukaryotic proteins, the amino group of the amino-terminal residue is Al-acetylated after translation. Carboxyl-terminal residues are also sometimes modified. 

The tendency for a (3 sheet to fold into a cylinder is encouraged in antiparallel (3 structures by the existence of a common irregularity called the (3 bulge.124 125 As illustrated in Fig. 2-18, a (3 bulge contains an extra residue inserted into one of the chains. In the second... 

The most relevant structural difference between the a and p monomers is located in the loop S9-S10, which is 8 residues longer in a-tub than in p-tub owing to an insertion. In the a-subunit, the long S9-S10 loop stabilizes the M loop. In the P-subunit, the equivalent position is occupied by the PTX binding site. This suggests that PTX mimics the 8-residue insertion of the a-subunit loop. In fact, the atomic model shows that the PTX molecule acts as a linker between helix H7 and the M loop, possibly stabilizing an M loop conformation that favors the lateral interprotofilament interaction and contributes to MT stabilization [24, 25], Both side chains and the baccatin core of PTX participate in these interactions [25],... 

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