Affinity chromatography of seminal plasma and sperm extracts
Representative graphic images of NHBP and HBP, purified from SP and SE are shown in Fig 1. HBP could be eluted from SP of 5, 3 and 5 bucks with 1M, 1.5M and 2.0M NaCl, respectively. In SE, it could be possible to elute HBP with 1.0M, 1.5M and 2.0M NaCl from 4, 5 and 4 bucks, respectively. Average area of NHBP / HBP peak was non-significantly (p>0.05) / significantly (p<0.05) higher in SP of G-II than G-I bucks (Table 1). However, an average HBP concentration was non-significantly high (23.8 vs. 20.6%) in SP of G-I compared to G-II, but the reverse was the case for NHBP. Average area of NHBP peak in SE was with mol. wt. of 22/30/38 kDa, 28/45/47 kDa, 24/34/55/59/70 kDa and 50/62/75 kDa showed a frequency distribution (FD) of 87.5%, 75%, 25% and 37.5% in sperm membrane proteins of Assam hill goats
(Deori et al., 2018).
Observations on area and protein concentration of heparin HBP and NHBP peaks indicated that area of peak was not proportional to the protein concentration in SP as well as SE. It can be predicted from these observations that quantity of SP-HBP and SE-HBP is related to SE-HBP. Variable fertility of bucks, which was more prominent in SE-HBP variable concentration of HBP was reported in SP of cross-bred cattle
(Srivastava et al., 2012, Cheema et al., 2016), buffalo
(Singh et al., 2014). Gupta et al., (2018) also reported an average HBP content of 2.04±0.098 mg/10
9 spermatozoa in buffalo bulls. Variations in HBP content of SP and SE was observed among the bucks during the present study as also reported in bulls (
Nauc and Manjunath, 2000 and
Gupta et al., 2018).
Characterization of seminal plasma and sperm proteins by SDS - PAG
SDS - PAGE of SP and SE resulted in resolution of 21 (10-240 kDa) and 21 (10-270 kDa) bands, respectively (Fig 2). Seventeen and sixteen protein bands were consistently present in SE and SP of Beetal bucks. However,
Deori et al., (2018) could separate 20 different proteins (10-75 kDa) with consistent pattern of only 6 proteins in spermatozoa of 8 Assam hill bucks. Sixteen protein bands ranging from 14-97 kDa were reported in SP of Anglo - Nubian goats
(Teixeria et al., 2006). Protein bands of 13, 15, 18 and 28 kDa in SE showed a distribution frequency of 68.5%, 31.8%, 92.8% and 69.2% in 13 Beetal bucks. Distribution frequency of 240, 90, 38, 28, 25 and 12 kDa peptides in SP was 76.9%, 53.9%, 53.9%, 84.6%, 84.6% and 23.1%, respectively. The proteins with mol. wt. of 22/30/38 kDa, 28/45/47 kDa, 24/34/55/59/70 kDa and 50/62/75 kDa showed a frequency distribution (FD) of 87.5%, 75%, 25% and 37.5% in sperm membrane proteins of Assam hill goats
(Deori et al., 2018).
Characterization of non - heparin (peak 1) and heparin (peak 2) bound proteins in seminal plasma by SDS - PAGE
Out of 14 bands detected in NHBP (10-180 kDa) and HBP (10-150 kDa), only ten and five bands were consistently observed in 13 bucks (Fig 3). FD of NHBPs of 35, 25 and 44 kDa was 53.8%, 46.1% and 7.7%, respectively (Table 2). HBPs of 25, 100/75 kDa, 35/10, 30, 28, 40 and 10 kDa showed a FD of 92.3%, 84.6%, 76.9%, 69.2%, 61.5%, 53.8% and 46.1% among the 13 bucks (Table 2). It indicated buck’s effect on SP- NHBP and HBP. La
Falci et al., (2002) identified HAP with mol wts of 73-104 kDa, 119 kDa and 178 kDa from goat SP.
Villemure et al., (2003) indicated the presence of GSP-14 kDa, GSP-15 kDa, GSP -20 kDa and GSP-22 kDa in goat SP by gelatin agarose chromatography but only GSP-20 and 22 kDa had affinity for heparin. But, in the present study, proteins of 13, 17, 20, 25 showed an affinity for heparin. Electrophoretic analysis of affinity purified HBP fraction from SP of Nellore bulls
(Fernandes et al., 2009), rams
(Martin et al., 2013), buffalo bulls
(Singh et al., 2014) and cross bred bulls
(Cheema et al., 2016) revealed the presence of 8 (15 - 63 kDa), 13 (10 - 232 kDa), 8/6/9 (13 - 71 kDa/14 - 61 kDa/10 - 170 kDa) and 14 (14-150 kDa) bands, respectively. Therefore, variation in number of HBP bands was also evident in other species.
Characterization of non-heparin binding and heparin binding proteins in sperm extracts by SDS-PAGE
NHBP and HBP purified from SE resolved into 11 bands ranging from 10-135 kDa and 10-120 kDa, respectively (Fig 4). Four and one band of NHBP and HBP were consistently detected in all bucks, respectively (Table 2). FD of 44/18 kDa, 85/50/25 kDa and 15 kDa non-HBP was 92.3%, 84.6% and 61.5%, respectively (Table 2). HBP’s of 120/20 kDa, 18 kDa, 50/45/37 kDa, 25/15 kDa and 31kDa showed a FD of 92.3%, 84.6%, 69.2% and 53.8% and 46.1%, respectively. Therefore, buck factor was also evident for variation in number of sperm NHBP and HBP.
Relationship of proteins and HBP in SP and SE with in vivo fertility
It was found that 20 kDa SP protein was present in all bucks except one exhibiting high FR and those of 15/13 kDa were absent in higher number (4/6 and 3/6) of G-1 compared to G-II bucks (3/7 and1/7). Another protein of 28 kDa was absent in 1/6 and 2/7 bucks of G-I and G-II, respectively. SE proteins of 2/6, 2/6, 4/6, 1/6, 1/6 and 3/6 bucks exhibiting high FR were devoid of 240, 90, 38, 28, 25 and 12 kDa proteins. These proteins were also not detected in 1/7, 4/7, 2/7, 1/7, 1/7 and 7/7 bucks, exhibiting low FR. Detection of 240 and 38 kDa proteins in higher number of G-I compared to G-II bucks indicated their role in fertility. Conversely, presence of 90 and 12 kDa proteins in higher number of G-II than G-I may be related to sub-fertility of bucks.
Nandi et al., (2012) did partial characterization of 14 kDa protein detected in goat spermatozoa and opined that it may play a crucial role in the acrosomal membrane fusion.
There was no difference in distribution of SP-NHBP among the two groups based on FR. However, difference in distribution of SP-HBP was observed among the bucks based on FR (Table 3). Number of SP-HBP bands constantly present in G-I and G-II bucks was eight and five, respectively. However, frequency distribution of 100/30/28 kDa and 40/13 kDa SP-HBP in G-I was 83.3% and 66.7%, respectively. A FD of 85.7%, 71.4%, 57.1%, 42.8% and 28.57% for 100/25 kDa, 75/40 kDa, 35/30 kDa, 26 kDa and 13 kDa HBP was noticed in SP-HBP of G-II bucks. It indicated that 75, 35, 30, 28, 25 and 13 kDa SP-HBP were present in higher (28.6%, 42.9%, 26.2%, 40.5%, 14.3% and 38.2%) number of G-I as compared to G-II bucks.
Two bands of SE-HBP were detected in all bucks of G-I (120/10 kDa) and G-II (18/10 kDa). FD for 53/50/45/20/18 kDa, 37/25 kDa and 31/15 kDa SE-HBP was 83.3%, 66.7% and 50% in G-I bucks (Table 3). However, FD of 120/20 kDa, 37 kDa, 50/45/31/15 kDa, 53/25 kDa in G-II was 85.71%, 71.4%, 57.1% and 42.8% respectively. It revealed that SE-HBP of 53 kDa, 50/45 kDa and 25 kDa were present in higher percentage (40.4%, 26.1% and 23.9%) of G-I than G-II bucks. SPP of bucks having affinity for heparin may be homologous to BSP proteins.
Villemure et al., (2003) also revealed that sequence of GSP-20 and 22 was homologous to BSP.
It may be predicted that SP-HBP and SE-HBP of 75, 35, 30, 28, 25, 13 kDa and 53, 50, 45 and 25 kDa are associated with higher fertility of Beetal bucks.
Mor et al., (2006) suggested that heparin binding moiety of sperm membrane protein may be required for modulation of sperm motility. Number of motile and viable spermatozoa were significantly (p<0.05) higher and MDA concentration was non-significantly low in GI bucks compared to G-II
(Dhillon et al., 2019). Therefore, SE-HBP of 53, 50, 45 and 25 kDa may have contributed to high sperm attributes
vis a vis fertility by reducing oxidative stress in G-I bucks. There is no supporting data regarding relationship of HBP with fertility in bucks, but HBP have been related to fertility of bulls
(Bellin et al., 1994, 1998 and
Sprott et al., 2000).