PDBsum entry 1os3

Hormone/growth factor

PDB id: 1os3

Contents

Protein chains

21 a.a.

29 a.a. *

28 a.a. *

Metals

_CL ×2

_ZN ×2

Waters ×40

* Residue conservation analysis

PDB id:

1os3

Name:

Hormone/growth factor

Title:

Dehydrated t6 human insulin at 100 k

Structure:

Insulin. Chain: a, c. Fragment: a-chain. Insulin. Chain: b, d. Fragment: b-chain

Source:

Homo sapiens. Human. Organism_taxid: 9606. Organism_taxid: 9606

Resolution:

1.95Å R-factor: 0.216 R-free: 0.253

Authors:

G.D.Smith,R.H.Blessing

Key ref:

G.D.Smith and R.H.Blessing (2003). Lessons from an aged, dried crystal of T(6) human insulin. Acta Crystallogr D Biol Crystallogr, 59, 1384-1394. PubMed id: 12876340 DOI: 10.1107/S090744490301165X

Date:

18-Mar-03 Release date: 29-Jul-03

Protein chains

P01308  (INS_HUMAN) -  Insulin from Homo sapiens

Seq: 110 a.a.

Struc: 21 a.a.

Protein chain

P01308  (INS_HUMAN) -  Insulin from Homo sapiens

Seq: 110 a.a.

Struc: 29 a.a.

Protein chain

P01308  (INS_HUMAN) -  Insulin from Homo sapiens

Seq: 110 a.a.

Struc: 28 a.a.

DOI no: 10.1107/S090744490301165X

Acta Crystallogr D Biol Crystallogr 59:1384-1394 (2003)

PubMed id: 12876340

Lessons from an aged, dried crystal of T(6) human insulin.

G.D.Smith, R.H.Blessing.

ABSTRACT

The structure of the T(6) hexameric form of human insulin has been determined at both room temperature and 100 K from a single air-dried crystal. At 100 K, the space group is R3 and the asymmetric unit consists of a dimer, as has been observed previously in hydrated structures. At room temperature, the space group is P1 and the unit cell contains a quasi-threefold-symmetric hexamer. In the absence of stabilizing water interactions, the N-termini of all six A chains in the room-temperature structure appear to have undergone partial unfolding, but the N-termini of these chains are well ordered in the 100 K structure. Other differences between the room-temperature and 100 K structures involve the coordination around the zinc ions. At 100 K, both zinc ions clearly exhibit dual coordination: zinc is octahedrally coordinated in one half of the zinc sites but tetrahedrally coordinated in the other half; at room temperature, the electron densities suggest tetrahedral coordination but the bond distances to the fourth ligands are longer than expected. Contrary to what has been observed to date in all other T(6) insulin structures, there are no contacts between pairs of GluB13 residues, either at room temperature or at 100 K, that would suggest the presence of a hydrogen bond. At room temperature, three of the six independent GluB13 side chains are disordered; at 100 K, both independent side chains are disordered. The disorder in the GluB13 side chains and the lack of contacts between carboxylate groups suggests that as a result of disruption of the hydration structure in the central core of the hexamer, all six B13 carboxylates bear a negative charge. This in turn suggests that in the hydrated structures the well ordered water structure in the central core is involved in stabilizing the B13 side-chain conformations and modulating charge repulsions among the six B13 glutamates if they are not protonated, or that, as is considered more likely, the water structure plays an important role in modulating the pK(a) values of the B13 glutamates, resulting in protonation and hydrogen-bond formation.

Selected figure(s)

Figure 7.
Figure 7 The 1 -contoured [A]-weighted (2F[o] - F[c]) electron density in the central core of the T[6] insulin hexamer in the rhombohedral structure of the dehydrated crystal at 100 K. The view is along the crystallographic threefold axis. The C^atoms (CG) are labeled on those GluB13 residues which are incomplete owing to disordered carboxylate groups. Prepared with the programs XtalView (McRee, 1999[McRee, C. E. (1999). J. Struct. Biol. 125, 156-165.]) and Raster3D (Merritt & Bacon, 1997[Merritt, E. A. & Bacon, D. J. (1997). Methods Enzymol. 277, 505-524.]).

Figure 8.
Figure 8 A schematic illustration of the packing of T[6] insulin hexamers in the hydrated R3 structure as viewed along the hexagonal c axis. Dashed lines denote the pseudo-twofold axes within the hexamers and the approximate boundary of each dimer. `A' and `B' label contact sites that contain five and six surface residues, respectively, that form nine interhexamer contacts of less than 3.4 Å, four of which are hydrogen bonds. Not shown are the contacts that exist between hexamers related by a translation along the c axis.

The above figures are reprinted by permission from the IUCr: Acta Crystallogr D Biol Crystallogr (2003, 59, 1384-1394) copyright 2003.

Figures were selected by an automated process.