I want to add field sort order in admin grid and in frontend part (sort by). I make module "news" and want to sort my news by title.

Please guide me how to do it

    protected function _prepareCollection()
    {
        $collection = Mage::getModel('mdnews/news')->getCollection();
        $this->setCollection($collection);
        return parent::_prepareCollection();
    }
    protected function _prepareColumns()
    {
        $helper = Mage::helper('mdnews');

        $this->addColumn('news_id', array(
        'header' => $helper->__('News ID'),
        'index' => 'news_id',
        'width' => '100px',
        ));

       $this->addColumn('title', array(
        'header' => $helper->__('Title'),
        'index' => 'title',
        'type' => 'text',
       ));

       $this->addColumn('category', array(
        'header' => $helper->__('Category'),
        'index' => 'category_id',
        'options' => $helper->getCategoriesList(),
        'type'  => 'options',
        'width' => '150px',
       ));

       $this->addColumn('created', array(
        'header' => $helper->__('Created'),
        'index' => 'created',
        'type' => 'date',
       ));

       return parent::_prepareColumns();
    }