Revisiting the structure of a synthetic somatostatin analogue for peptide drug design

Abstract

Natural or artificially manufactured peptides attract scientific interest worldwide owing to their wide array of pharmaceutical and biological activities. X-ray structural studies are used to provide a precise extraction of information, which can be used to enable a better understanding of the function and physicochemical characteristics of peptides. Although it is vulnerable to disassociation, one of the most vital human peptide hormones, somatostatin, plays a regulatory role in the endocrine system as well as in the release of numerous secondary hormones. This study reports the successful crystallization and complete structural model of octreotide, a stable octapeptide analogue of somatostatin. Common obstacles in crystallographic studies arising from the intrinsic difficulties of obtaining a suitable single-crystal specimen were efficiently overcome as polycrystalline material was employed for synchrotron and laboratory X-ray powder diffraction (XPD) measurements. Data collection and preliminary analysis led to the identification of unit-cell symmetry [orthorhombic, P2 1 2 1 2 1 , a = 18.5453 (15), b = 30.1766 (25), c = 39.798 (4) Å ], a process which was later followed by complete structure characterization and refinement, underlying the efficacy of the suggested (XPD) approach.

In situdetection of a novel lysozyme monoclinic crystal form upon controlled relative humidity variation

“…Although X-ray powder diffraction (XRPD) structural studies of small organics and inorganics upon rH variation is a routine practice, this is not the case for proteins. However, advances in instrumentation (Margiolaki, Wright, Fitch et al, 2007), data collection and analysis approaches (Margiolaki & Wright, 2008;Karavassili & Margiolaki, 2016;Karavassili et al, 2017) have established XRPD as a powerful complementary tool for quick and accurate protein crystal screening as well as polymorph identification (Von Dreele et al, 2000;Hunter et al, 2011;Karavassili et al, 2012;Fili et al, 2015Fili et al, , 2016Karavassili & Margiolaki, 2016;Valmas et al, 2015Valmas et al, , 2017Logotheti et al, 2019) and structure determination (Margiolaki et al, 2005(Margiolaki et al, , 2013Margiolaki, Wright, Wilmanns et al, 2007;Fili et al, 2019). XRPD is ideal as it allows for investigation of microcrystalline samples (average crystallite size <5 mm) as an ensemble rather than individual crystals which may not represent the bulk material.…”

Applications of X-ray Powder Diffraction in Protein Crystallography and Drug Screening

“…Additional measurements were performed on the MS-X04SA beamline at the SLS [157] in Villigen, where samples were measured at RT using a wavelength of 1.3004392 (8) Å (dres_SLS = 1.87 Å) and a position-sensitive Mythen II detector (Figure 15). Owing to the fact that the latest crystallographic study of this peptide was performed back in 1995 [153], our research team decided to conduct new XRPD measurements of freshly prepared polycrystalline specimens, in order to elucidate the three-dimensional arrangement of the peptide aiming towards the examination of its properties and the investigation of the existence of different polymorphs [34]. Additionally, in the abovementioned study, it is discussed if the polycrystalline precipitates produced could be employed in the production of longer-lasting formulations of the specific molecule.…”

“…Additional measurements were performed on the MS-X04SA beamline at the SLS [157] in Villigen, where samples were measured at RT using a wavelength of 1.3004392 (8) Å (dres_SLS = 1.87 Å) and a position-sensitive Mythen II detector ( Figure 15). Indexing revealed the presence of the orthorhombic crystal symmetry (space group: P2 1 2 1 2 1 , a = 18.5453 (15) Å, b = 30.1766 (25) Å and c = 39.798 (4) Å) while data quality allowed for the complete structure determination using the FRB approach in GSAS program [34] (Figure 16).…”

“…Indexing revealed the presence of the orthorhombic crystal symmetry (space group: P212121, a = 18.5453 (15) Å, b = 30.1766 (25) Å and c = 39.798 (4) Å) while data quality allowed for the complete structure determination using the FRB approach in GSAS program [34] (Figure 16).…”

“…A pharmaceutical composition may consist of more than one component, each of which is an active pharmaceutical ingredient [33]. XRPD is extensively used for the identification of specific components when examining intermixtures of inorganics or small organics, while its applicability is steadily increasing in the context of characterizing new pharmaceutically important phases of biological macromolecules which, in combination with the crystalline nature of the corresponding compound, may display advantageous properties as increased solubility and prolonged release of the beneficial agent [24,34]. The crystalline properties of individual polymorphs and their direct correlation with a drug's absorption, distribution, metabolism and excretion (ADME) characteristics can lead to the production of more efficient, or macromolecular, formulations with alternative methods of delivery such as sustained-release or inhaled compounds [35].…”