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. 2017 Mar 29;22(4):544.
doi: 10.3390/molecules22040544.

A Specific Peptide with Calcium-Binding Capacity from Defatted Schizochytrium sp. Protein Hydrolysates and the Molecular Properties

Xixi Cai  1   2 , Qian Yang  3   4 , Jiaping Lin  5 , Nanyan Fu  6 , Shaoyun Wang  7
Affiliations

A Specific Peptide with Calcium-Binding Capacity from Defatted Schizochytrium sp. Protein Hydrolysates and the Molecular Properties

Xixi Cai et al. Molecules. .

Abstract

Marine microorganisms have been proposed as a new kind of protein source. Efforts are needed in order to transform the protein-rich biological wastes left after lipid extraction into value-added bio-products. Thus, the utilization of protein recovered from defatted Schizochytrium sp. by-products presents an opportunity. A specific peptide Tyr-Leu (YL) with calcium-binding capacity was purified from defatted Schizochytrium sp. protein hydrolysates through gel filtration chromatography and RP-HPLC. The calcium-binding activity of YL reached 126.34 ± 3.40 μg/mg. The calcium-binding mechanism was investigated through ultraviolet, fluorescence and infrared spectroscopy. The results showed that calcium ions could form dative bonds with carboxyl oxygen atoms and amino nitrogen atoms as well as the nitrogen and oxygen atoms of amide bonds. YL-Ca exhibited excellent thermal stability and solubility, which was beneficial for its absorption and transport in the basic intestinal tract of the human body. Moreover, the cellular uptake of calcium in Caco-2 cells showed that YL-Ca could enhance calcium uptake efficiency and protect calcium ions against precipitation caused by dietary inhibitors such as tannic acid, oxalate, phytate and metal ions. The findings indicate that the by-product of Schizochytrium sp. is a promising source for making peptide-calcium bio-products as algae-based functional supplements for human beings.

Keywords: Schizochytrium sp.; calcium-binding peptide; cellular uptake; defatted protein hydrolysate; mechanism.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Chromatography elution profiles and calcium binding capacities of calcium-binding peptides. (A) Sephadex G-25 gel filtration chromatography of SPH; (B) Semi-preparative C18 RP-HPLC of fraction III; (C) RP-HPLC of fraction 17 from semi-preparative HPLC.
Figure 2
Figure 2
Identification of the amino acid sequence of the calcium-binding peptide using LC-ESI-MS/MS.
Figure 3
Figure 3
Ultra-violet spectra of YL with different CaCl2 concentration.
Figure 4
Figure 4
Fluorescence spectra of YL with different CaCl2 concentrations.
Figure 5
Figure 5
FTIR spectra of YL and YL-Ca chelate.
Figure 6
Figure 6
Typical TG-DSC thermograms of (A) YL and (B) YL-Ca chelate.
Figure 7
Figure 7
Calcium-releasing percentage of YL-Ca chelate and CaCl2 at different pH.
Figure 8
Figure 8
Cellular uptake of YL-Ca chelate and CaCl2 in Caco-2 cell model. (A) Cell uptake of YL-Ca chelate in Caco-2 cell by Fluo-3-AM loading for fluorescence analysis; (B) Effect of YL-Ca chelate on cellular uptake of calcium under the action of dietary inhibitors. The concentration of calcium was 10 mM and tannic acid/Ca, oxalate/Ca, phytate/Ca or Zn/Ca = 20:1. * Statistical significance p < 0.05, compared with CaCl2 control group. # Statistical significance p < 0.05, compared with YL-Ca control group.
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