Loop anchor modification causes the population of an alternative native state in an SH3-like domain.

Many stably folded proteins are proposed to contain long, unstructured loops. A series of hybrid proteins (EbE1-4) containing the folded scaffold of photosystem I accessory protein E (PsaE), an SH3-like protein, and the 40-residue heme-binding loop of cytochrome b(5) was created to inspect the dependence of thermodynamic and kinetic parameters on the residues at the interface of folded and flexible regions. Compared to the simplest hybrid (EbE1), the chimeras differed by Gly insertions (EbE2, EbE3) or an asymmetric four-residue restructuring of loop termini (EbE4).

Proximal influences in two-on-two globins: effect of the Ala69Ser replacement on Synechocystis sp. PCC 6803 hemoglobin.

The cyanobacterium Synechocystis sp. PCC 6803 (S6803) expresses a two-on-two globin in which His46 (distal side) and His70 (proximal) function as heme iron axial ligands. His46 can be displaced by O2, CO, and CN-, among others, whereas His70 is not labile under native conditions.

Insertion of the cytochrome b5 heme-binding loop into an SH3 domain. Effects on structure and stability, and clues about the cytochrome's architecture.

Under native conditions, apocytochrome b(5) exhibits a stable core and a disordered heme-binding region that refolds upon association with the cofactor. The termini of this flexible region are in close proximity, suggesting that loop closure may contribute to the thermodynamic properties of the apocytochrome. A chimeric protein containing 43 residues encompassing the cytochrome loop was constructed using the cyanobacterial photosystem I accessory protein E (PsaE) from Synechococcus sp.

A buried polar residue in the hydrophobic interface of the coiled-coil peptide, GCN4-p1, plays a thermodynamic, not a kinetic role in folding.

The hydrophobic interfaces of coiled-coil proteins and peptides are typically interspersed with buried polar residues. These polar residues are known to be important for defining oligomeric specificity and chain orientation in coiled-coil formation; however, their effects on the folding/assembly reaction have not been investigated. The commonly studied 33-residue dimeric leucine zipper peptide, GCN4-p1, contains a single polar Asn in the center of the hydrophobic interface at position 16.