Most of bioinformatics data distributed on the Internet is organized in an unstructured manner, which makes it hard to construct applications that need to integrate them. In this paper, we proposed an XML schema based data indexing mechanism to integrate sequence databases stored in a DHT overlay network. The construction of large-scale distributed applications therefore can be greatly simplified with the support of structured distributed data. We present a system that can seamlessly integrate sequence databases and computing resources together to provide BLAST query services based on the data indexing mechanism. Our experiments show that, with a data centric scheduling algorithm to improve the processor utilization, the BLAST service can achieve scalable high throughput.