title: Influence of semisynthetic modification of the scaffold of a contact domain of HbS on polymerization: role of flexible surface topology in polymerization inhibition.
abstract: A new variant of HbS, HbS-Einstein with a deletion of segment α23-26in the B-helix, has been assembled by semisynthetic approach. B-helix of the α chain of cis αβ-dimer of HbS plays dominant role in the quinary interactions of deoxy HbS dimer. This B-helix is the primary scaffold that provides the orientation for the side chains of contact residues of this intermolecular contact domain. The design of HbS-Einstein has been undertaken to map the influence of perturbation of molecular surface topology and the flexibility of surface residues in the polymerization. The internal deletion exerts a strong inhibitory influence on Val-6 (β)-dependent polymerization, comparable to single contact site mutations and not for complete neutralization of Val-6(β)-dependent polymerization. The scaffold modification in cis-dimer is inhibitory, and is without any effect when present on the trans dimer. The flexibility changes in the surface topology in the region of scaffold modification apparently counteracts the intrinsic polymerization potential of the molecule. The inhibition is close to that of Le Lamentin mutation [His-20 (α) → Gln] wherein a mutation engineered without much change in flexibility of the contact domain. Interestingly, the chimeric HbS with swine-human chimeric α chain with multiple non-conservative mutations completely inhibits the Val-6(β)-dependent polymerization. The deformabilities of surface topology of chimeric HbS are comparable to HbS in spite of the multiple contact site mutations in the α-chain. We conclude that the design of antisickling Hbs for gene therapy of sickle cell disease should involve multiple mutations of intermolecular contact sites.
authors.affiliation: a Division of Hematology , Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York 10461 , USA.
authors.forename: Srinivasulu
authors.initials: S
authors.lastname: Sonati
authors.affiliation: a Division of Hematology , Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York 10461 , USA.
authors.forename: Savita
authors.initials: S
authors.lastname: Bhutoria
authors.affiliation: a Division of Hematology , Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York 10461 , USA.
authors.forename: Muthuchidambaran
authors.initials: M
authors.lastname: Prabhakaran
authors.affiliation: a Division of Hematology , Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York 10461 , USA.|b Department(s) of Medicine and of Physiology and Biophysics , Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York 10461 , USA.
authors.forename: Seetharama A
authors.initials: SA
authors.lastname: Acharya
mesh_terms: D000818:Animals; D006451:Hemoglobin, Sickle / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D009154:Mutation; D058105:Polymerization; D011108:Polymers / Q000737:chemistry*; D011487:Protein Conformation; D013552:Swine
chemical_list: D006451:Hemoglobin, Sickle; D011108:Polymers; C038875:deoxyhemoglobin, sickle
keywords: Flexibility; gene therapy of sickle cell disease; polymerization; protein surface-topology; semisynthetic internal-deletion