1. An evaluation of the effect of hydrofluoric acid (HF) treatment on keratins
Tao Zhao, Yanhong Pan J Exp Zool B Mol Dev Evol. 2022 Aug 24. doi: 10.1002/jez.b.23173. Online ahead of print.
Hydrofluoric acid (HF) is commonly used in geological and paleontological research to extract organic fossils for morphological and chemical studies. However, during HF treatment, organic matter can also be altered, which raises concerns that HF-treated organic matter may not be representative of the original organic matter. To provide reference data for protein studies on fossils, herein, we use Fourier transform infrared (FTIR) spectroscopy to investigate the effect of HF (21.3 M) treatment on keratins, with treatment durations ranging from 2 to 48 h. Results show that the FTIR spectra of HF-treated samples are overall similar to that of the untreated sample, while curve fitting shows that HF treatment has led to alteration of the secondary structure in all the HF-treated samples and the effect is time-dependent. The 2- and 4-h treatment mainly reduced the content of the random coils, α-helix, and intermolecular β-sheet. From 8h onwards, the content of random coils greatly increased at the expense of other structures. Our results imply that for protein detection in fossils using FTIR spectroscopy, the negative effect of HF treatment is not substantial, as the bands characteristic of proteins, that is, amide A, amide B, amide I, amide II, and amide III, are still present after the 48-h treatment. If the target is a secondary structure, the effect of HF treatment should be considered. When HF treatment is necessary, limiting the treatment duration to less than 4h may be a choice.
2. Characteristics and Properties of Acid- and Pepsin-Solubilized Collagens from the Tail Tendon of Skipjack Tuna ( Katsuwonus pelamis)
Sagun Chanmangkang, Sutee Wangtueai, Nantipa Pansawat, Pramvadee Tepwong, Atikorn Panya, Jirawan Maneerote Polymers (Basel). 2022 Dec 6;14(23):5329. doi: 10.3390/polym14235329.
The tail tendons of skipjack tuna (Katsuwonus pelamis), a by-product from the meat-separation process in canned-tuna production, was used as an alternative source of collagen extraction. The acid-solubilized collagens using vinegar (VTC) and acetic-acid (ATC) extraction and pepsin-solubilized collagen (APTC) were extracted from tuna-tail tendon. The physiochemical properties and characteristics of those collagens were investigated. The obtained yield of VTC, ATC, and APTC were 7.88 ± 0.41, 8.67 ± 0.35, and 12.04 ± 0.07%, respectively. The determination of protein-collagen solubility, the effect of pH and NaCl on collagen solubility, Fourier-transform infrared spectroscopy (FTIR) spectrum, and microstructure of the collagen-fibril surface using a scanning electron microscope (SEM) were done. The protein solubility of VTC, ATC, and APTC were 0.44 ± 0.03, 0.52 ± 0.07, and 0.67 ± 0.12 mg protein/mg collagen. The solubility of collagen decreased with increasing of NaCl content. These three collagens were good solubility at low pH with the highest solubility at pH 5. The FTIR spectrum showed absorbance of Amide A, Amide B, Amide I, Amide II, and Amide III groups as 3286-3293 cm-1, 2853-2922 cm-1, 1634-1646 cm-1, 1543-1544 cm-1, and 1236-1237 cm-1, respectively. The SEM analysis indicated a microstructure of collagen surface as folding of fibril with small pore.
3. Bioactive Bromotyrosine Alkaloids from the Bahamian Marine Sponge Aiolochroia crassa. Dimerization and Oxidative Motifs
Mariam N Salib, Rudi Hendra, Tadeusz F Molinski J Org Chem. 2022 Oct 7;87(19):12831-12843. doi: 10.1021/acs.joc.2c01415. Epub 2022 Sep 16.
Nine bromotyrosine alkaloids (BTAs), including debromoianthelline (1), pseudoceratinic acid (2a), methyl pseudoceratinate (2b), 13-oxo-ianthelline (3), aiolochroiamides A-D (4a,b and 5a,b), and 7-hydroxypurealidin J (6), were isolated from a Bahamian Aiolochroia crassa (Hyatt; previously, Pseudoceratina crassa). The structures of 1-6 were established from 1H, 13C, and 2D NMR spectra, IR, and mass spectrometry data. Compounds 2-4 comprise an O-methyl-2,6-dibromotyrosyl ketoxime (subunit A) amide linked to variable groups (subunit B). Compound 1 is debromoianthelline, and 2a and 2b are amides of 3-aminopropanoic acid and methyl 3-aminopropanoate, respectively. BTAs 3 and 4 are linked to 5-(2-aminoethyl)-2-iminoimidazolidin-4-one and a hexahydropyrrolo[2,3-d]imidazol-2(1H)-imine nucleus, respectively, whereas 5 is a self-dimerization motif of an aryl pyruvamide. Alkaloid 6 contains a spirocyclohexadienyl-isoxazoline-carboxamide amide coupled to 2-aminohistamine similar to that found in purealidin J and aerophobin-1 but with hydroxylation at C-7. The 2,4-diaminobutanoic acid residue in 3 was determined to be a 2:1 L- and D- mixture based on hydrolysis followed by derivatization with L-FDTA and LCMS. Diastereomeric pairs, 4a,b and 5a,b, were racemic. The relative configurations of 4a, 4b, 5a, and 5b were assigned by comparison of 1H and 13C chemical shifts with those calculated by DFT. Compounds 5a,b, ningalamide B (9), and ianthelline (7) moderately inhibited butyrylcholinesterase and Candida and Cryptococcus spp.
